Air conditioner or heat pump noise descriptions linked to problem diagnosis & cure recommendations.

We have grouped HVAC system noises into groups by noise type and in alphabetic order using words suggested by our readers in describing various noise types, their probable cause and proper repair.

This air conditioning repair article discusses the diagnosis and repair of air conditioning compressor noises which range in importance from normal (if annoying squeaks and squeals, to rattling loose bolts and hardware, to costly compressor damage indicating air conditioning compressor or A/C compressors at or near end of their life.

Page top: an outdoor compressor/condenser unit more than 30 years old, still working normally. Motor noise and fan noise are normal at compressor/condenser units, but abnormal sounds like those listed below range from banging to whistling or "wuwwu" and indictate that repair is needed.

Catalog of Air Conditioner or Heat Pump Noises by Description of the Sound

Here is an index to all of the diagnostic sounds or noises you may hear at an air conditioner or heat pump system either outdoors at the compressor/condenser unit or indoors at the air handler / blower unit or perhaps in the ductwork itself.

Keep in mind that some of these sounds may occur together and also that people may describe the same sound using different words.

One person's banging noise may be thumps or clunks to another while hissing and screeching and screaming may also be mixed-up together.

This means you may want to read about the causes and cures listed for several of the HVAC system noise articles listed here.

Photo: abnormal noises can occur at the outdoor compressor/condenser unit (shown just above), or indoors at the air handler or ductwork or at a wall-mounted split system A/C or heat pump. Abnormal HVAC noises also include sounds coming from refrigerant piping that connect the indoor to outdoor unit.

Index to Text Descriptions of A/C or heat pump sounds & possible causes / cures

• NOISES, HVAC SYSTEM DIAGNOSIS - home
• NOISES, HVAC SOUND DESCRIPTIONS
  • HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping
    • BANGING A/C or heat pump
    • BANGING NOISE at AIR HANDLERS or in DUCT SYSTEMS
    • BEARING NOISES in HVAC equipment or motors
    • BUZZING SOUNDS & vibration sounds from A/C, heat pump or inverter or from other equipment in, or, or near buildings
    • BUZZING NOISE DIAGNOSIS REPAIR - topic home
  • HVAC NOISE-2 CHATTER CHIRP CLANK FAN GRIND GROAN - chatter, chirp, clank, clunk, cyclical, fan, fog horn, honk, moan, grinding, groan, growl
    • CHATTERING RELAY CONTROL SWITCHES
    • CHIRPS or CHIRPING sounds at the air conditioner or A/C control
    • CLANKS CLUNKS from air conditioner or heat pump system
    • CLICKING SOUNDS from air conditioner or heat pump system - also see FAN NOISES, HVAC - including ticking - also see HVAC TICKING NOISE DIAGNOSIS
    • CYCLICAL REGULAR NOISES or vibrations
    • FAN NOISES wobbles, motor hum, depending on speed
    • GRINDING NOISES failing bearings, controls, dampers or other sources in buildings
    • GROANING sounds from A/C or heat pump system, diagnosis
    • GROWLING compressor sounds (also see Groaning above)
    • GURGLING SOUNDS from the AC or refrigerant piping
    • HONKING SOUNDS at the A/C or Heat Pump system
  • HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff or humming noises
    • HISSING SOUNDS, HVAC from A/C or heat pump system
    • HOWLING SOUNDS, HVAC from air conditioners, air handlers, blower fans, heat pumps, furnaces, duct systems & their motors
    • HUFFING sounds from A/C or heat pump system, diagnosis
    • HUMMING sounds from A/C or Heat Pump system
    • HUMMING NOISES in BUILDINGS - topic home
  • HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, popping, rattling, roaring, rumbling, running water
    • LOUD NOISE at STARTUP then quiet HVAC equipment
    • POPPING or POPCORN noises - turn off the system immediately
    • RATTLING & VIBRATION noises from A/C or Heat Pump System
    • ROARING NOISE from A/C Compressor/Condenser unit
    • RUMBLING NOISES A/C compressor/condenser or blower fan motor noise
    • RUNNING WATER sounds in refrigerant piping - floodback or condensate?
  • HVAC NOISE-5 SCREAM SING TICKING TRUMPET WHINE WUWU - high pitched noise, tick, scream, sing, squeal, trumpet, water sounds, whine, wuwuwu
    • SCREAMING SOUNDS at HVAC A/C compressor/condenser unit sounds - warning!
    • SILENCE no sound whatever coming from HVAC equipment?
    • SINGING, rumbling, whining A/C compressor/condenser or blower fan motor noise
    • SQUEALING air conditioner and heat pump equipment, diagnosis
    • TICKING NOISE DIAGNOSIS
    • TRUMPETING noises from compressor motors on A/C and heat pump systems
    • WaWa, Wow wow sounds from A/C or heat pump system, diagnosis
    • WATER SOUNDS in HVAC refrigerant piping or coils
    • WHINING A/C compressor/condenser or blower fan motor noise
    • WHOOSHING SOUNDS from the expansion valve
    • WHISTLING sounds at HVAC air handler or ductwork
    • WU WU WU sounds from A/C or heat pump system, diagnosis
  • NOISES, HVAC SOUND RECORDINGS
• NOISE / SOUND DIAGNOSIS & CURE - home

Index to Recordings of A/C or Heat Pump Sounds & Noises: Submit, Listen-to, or Comment on These Sounds

BUZZING, intermittent sound video at the outdoor AC or HEAT PUMP fan/compressr unit of a heat pump whose compressor motor is unable to start

- web article NOISES, HVAC SYSTEM DIAGNOSIS includes video

Intermittent buzzing sound / video

A brief video contributed by one of our readers [OFFLINE 2020/01/20 for security] demonstrates start-up troubles and characteristic buzzing at the outdoor fan-compressor unit. The unit is unable to start.

Some guesses at what the noise means are given below.

Other videos: VIDEO GUIDES at InspectAPedia.com

BUZZ RATTLE SOUND RECORDING, - 600KB MP3 file - possible liquid refrigerant slugging sound occurs about 10 seconds into recording - sound recording .mp3 file Liquid slugging can also sound like rocks rattling around in a metal can or like a metallic clattering.

BUZZING RATTLING Kenmore AIR CONDITIONER NOISE RECORDING - buzz, rattle, hard-start - sound recording .mp3 file

Squealing, clanking compressor noises

One of our readers (L.M.) CITED [VIDEO OFFLINE FOR SECURITY 2020/01/20] start-up troubles and loud continuous squealing, clanking, and what I take to be some humming at the outdoor fan-compressor unit. The unit is unable to start and run normally.

A/C Compressor Noise Description:

Twice in the last month in a half, we’ve had this squealing metallic noise coming from the exterior condenser.  On both occasions the AC was running fine all day, then about 930 or 10 PM it starts making this noise.  In both cases it eventually stopped making the noises on its own.  It makes the noise only while AC is running.  Fan only is OK.

Some guesses at what the noise means are given below at Squealing air conditioner and heat pump equipment, diagnosis

• SANYO SPLIT SYSTEM OUTDOOR COMPRESSOR UNIT - 840K .wav file - normal operation, with some air or wind noise at the microphone - sound recording .wav file
• SANYO SPLIT SYSTEM INDOOR COOLING UNIT, wall-mounted - 790K .wav file - normal operation, with some air noise at the microphone - sound recording .wav file
• GAS REGULATOR NOISES includes a description of humming buzzing sounds at a gas fired water heater
• Contact Us to submit an air conditioner or heat pump system noise or sound recording for posting, analysis, or to offer a comment about one of the air conditioner/heat pump noise recordings found here

HVAC Noise Group 1 Banging

Banging Sounds from A/C Compressor or Heat Pump, Frequent Compressor Replacements?

Common sources of loud banging, clanging or clanking noises at an air conditioner or heat pump include the following:

• Failing compressor motor, possibly a broken piston or connecting rod, or broken pin connecting the piston to the connecting rod, or perhaps a failing motor crankshaft - depending on motor design. None of these parts are field-repairable.
  
  Also see SCREAMING SOUNDS at HVAC A/C compressor/condenser unit sounds - and see our warning below!
• Failing motor bearing noise may result in banging, more often other sounds.
  
  Also see BEARING NOISES in HVAC equipment or motors
• Loose components such as a loose motor or parts in the condenser unit
• Fan blade loose on motor shaft or blades bent,
  
  hitting the condensing unit case or in an air handler hitting components in the blower compartment. Fan blades may also bang into ice forming on the outdoor unit or on an obstuction fallen into the unit - the kids jammed a stick into the condenser unit fan cage.
• Also see CLANKS CLUNKS from air conditioner or heat pump system

Watch out: you should immediately turn off equipment making these noises. Moving parts can cut wires risking fire or shock, or a loose fan can cut a refrigerant line or cause other more costly damage to the system. Always call for repair by a trained HVAC service technician.

Banging or Hard Starting Compressor Condenser Unit Video

BANGING HARD-STARTING COMPRESSOR FAN - MP4 file recording.

Banging Noises at the Air Handler or in Duct Systems

A loud BANG or THUD or CLUNK heard when the heating or air conditioning blower fan starts or stops is often due to inadequate return air, to overpressureizing of the supply plenum at fan start-up, or it may occur where large areas of un-supported sheet metal are used in the duct system or air supply or return plenums.

The problem may be more acute where a multiple speed or high speed blower fan is in use.

What Causes the BANG at Blower Fan Start-Up or Shut-Down?

When the fan starts up the system is at least initially a bit air-starved creating a vacuum on the return side of the system. A powerful fan can also cause the same noise by bulging out rather than in sheet metal components on the supply side of the heating or cooling system.

Once the sheet metal has been bulged out by the pressure of supply air, when the blower fan stops we may hear a second BANG or CLUNK noise. In fact at a cabin we recently rented at the Sleeping Giant campground the shut-down noise seemed louder than the start-up noise, probably because it was not partly obscured by the noise of the blower fan itself.

How to Fix Start-up or Shut-down Air Handler BANGING

• If the system is truly air-starved then it makes a lot of sense to add more return air inlets since not only will you be curing the start-up or shut-down BANG noise in the duct and air handler system but you'll also improve the effectiveness and efficiency of the system.
  
  See RETURN AIR, INCREASE
  
  And
  see UNDERSIZED RETURN DUCTS
• If the problem is a powerful fan at start-up but no air-starved concerns, then I would add reinforcement U-channel to stop flexing sheet metal noises.
• If the system is not air-starved, a fan control that ramps up the fan speed improves the situation but that's not a normal control.
• Running the fan always on the lower speed defeats the purpose of having a multiple speed or variable speed blower fan in the first place: different speeds for varying needs. I don't recommend that as a long term solution.
• See SOUND CONTROL for AIR DUCTS, HVAC for other sound control suggestions.
• If the BANG occurs outside at the heat pump or air conditioner compressor/condenser unit,
  
  see BANGING A/C or heat pump

Other furnace or air conditioning duct noises such as hissing and howling can be from air velocity combined with duct shape, size, bends, or obstuctions, or from leaks in the duct system. For those see

• HISSING SOUNDS, HVAC from A/C or heat pump system
• HOWLING SOUNDS, HVAC from air conditioners, air handlers, blower fans, heat pumps, furnaces, duct systems & their motors

A Simple DIY test for Inadequate Return Air

When you have to leave the a blower compartment door open then it's a pretty good indicator that the system needs more return air.

Another similar test I make is to wait until the blower has been on for 5 minutes or more, then open the air handler blower compartment door about 6" and let go. If the door SLAMS shut with a powerful BANG then the system is probably air starved.

Bearing Noises in HVAC equipment

Reader Question:

Sounds like very loud bering noise on start up and shut down from a 1 year old heat pump compressor - Ray 12/5/11

Reply:

Ray, a bearing noise, often a horrible clanking, banging, or rattling, is generated by a wobbling of a rotating shaft that is no longer evenly supported by bearings that are intended to permit it to rotate with minimal friction. A bad motor bearing can also cause a squealing or screeching noise, and if the bearing and motor shaft actually begin to bind you may hear a humming or buzzing from the electric motor.

If you hear bearing noises from an A/C compressor motor I suspect that the motor is failing, or that a similar noise is being made by damaged refrigerant valves in the compressor head. But first check that the motor mounts are secure.

Sometimes a motor can make a clank or thunk at startup because one or more of its mounts has come loose.

Watch out: Shut off any electric motor that is screeching, humming, or running as described above. Then call for repair.

Buzzing Sounds at Air Conditioning or Heat Pump Equipment

This page addresses buzzing or vibration noises at air conditioners or heat pumps.

For other types of equipment buzzing and vibration sound complaints see

• HEATING SYSTEM BUZZING NOISE
• OIL LINE BUZZ & VIBRATION CURE
• NOISE, WATER HEATER - more buzzing & other noises
• WATER PUMP PRESSURE SWITCH NOISES - including buzzing and vibration noises

Common sources of buzzing noises or sounds at the air conditioner / heat pump unit or other equipment in a building

1. Loose or missing isolation feet 
   
   on the compressor motor itself or on the whole compressor/condenser unit.
   
   Check that both the motor and the whole outdoor unit a level and all feet are pressing on the support pad. You may need help from a trained service tech to remove the coer and then to inspect the interior of a compressor/condenser unit to see the isolation pads under the compressor motor.
2. Bad relay control switch or contactor relay:
   
   Bad or failing compressor motor relay switch or bad fan contactor relay switch may buzz or hum.
   
   These are usually low-voltage (e.g. 24VAC) controls that are used to switch on the higher-voltage-operated motors of the compressor and fan.
3. Loose components,
   
   screws, cabinetry, grilles, on the compressor/condenser unit outdoors or on the air handler indoors; also loose or poorly supported refrigeration piping or electrical wiring conduit that may contact and buzz against another surface as the equipment vibrates
4. Fan motor failures:
   
   Bad or failing condenser fan motor on the compressor/condenser unit may buzz or hum and may fail to start.
   
   Similarly a bad fan motor in the air handler unit or blower unit can hum or buzz. Remeber to check the fan itself for mechanical damage, wobbling, bent blades as those can cause vibration that first shows up as noise but ultimately damages the motor bearings.
5. Compressor motor failures:
   
   A compressor motor that tries to start but cannot get running may buzz or hum for a few seconds before its overload switch shuts down the motor.
   
   Low voltage or a bad start/run capacitor can also prevent an electric motor from starting successfully.
   
   Don't rush to replace a compressor motor when you hear buzzing noises as a mis-diagnosis can lead to an expensive and incorrect repair. Check other components in the system with care.
6. Refrigerant leak or bad TEV:
   
   Refrigeration leak or low refrigeration charge causing icing anywhere in the system; Ice-blockage of a themostatic expansion valve (TEV) or electronic expansion valve (EEV) can cause buzzing noises as refrigerant passes through the device.
7. Bad or clogged filter dryer 
   
   canister at the HVACR unit
8. Improper voltage,
   
   possibly low voltage, causing motors to have trouble starting: motors or contactors may hum or buzz. A bad start/run capacitor can also leave a motor buzzing but more often humming.
   
   Voltage drops or transients can cause motors to have trouble starting but may not be present when the service tech examines the system. Monitoring voltage levels may be necessary to find intermittent motor start or motor buzzing problems.
9. Defective fuse or circuit breaker
   
   at the service switch or power control for the unit; Bad, defective, loose electrical connections causing arcing, humming, buzzing, crackling sounds, possibly smoke or odors as well.
   
   Watch out: corroded aluminum feeder wires, loose electrical connections, wet, rusted or damaged circuit breakers, improper fusing or similar electrical defects at the fuse or local service switch for an air conditioner or heat pump may cause worse than hissing or buzzing, risking as well an electrical shock or fire hazard.
10. Loose electrical connections
    
     inside the equipment. A loose clip-on connector bringing power to a start/run capacitor or to a control relay can cause buzzing sounds in the equipment.
11. Normal buzzing at the reversing valve:
    
    If your unit is a heat pump then check the solenoid coil switch that operates the reversing valve on your system - really ask your service tech to make these checks.
    
    For some heat pump systems the reversing valve solenoid may buzz for a time when the system stops operating - pressures are equalizing. It's normal.
12. Air Handler Noises:
    
    AIR HANDLER / BLOWER NOISES for a discussion of noisy furnace or air conditioner air handlers or ductwork noises such as air leaks, clicking, thumping or banging duct noises, fan noises and vibration dampener noises or rattling at fan motors
13. Duct System Noises:
    
    DUCT SYSTEM NOISES rattling & buzzing from loose components, if the noise is coming from or being transmitted by ductwork.
14. More buzzing noises from heating equipment
    
    like furnaces, boilers, water heaters, are described at
    
    HEATING SYSTEM BUZZING NOISE and
    
    at OIL LINE BUZZ & VIBRATION CURE
15. More buzzing noises from a water heater are
    
    at NOISE, WATER HEATER
16. More buzzing noises from a water pump are
    
    at WATER PUMP PRESSURE SWITCH NOISES

Diagnostic tips for a buzzing air conditioner or heat pump

• Check to see if you can trace the noise to the reversing vavle.
• Inspect the unit for loose parts or damaged isolation feet; try touching or holding possibly loose components to see if the noise stops. DO NOT stick fingers into areas where there are moving parts or they'll get chopped off.
• Listen to the noise to try to isolate its source; Use a mechanics' sthethoscope to home in on a noise source.
• Turn off electrical power to the unit. Be sure power is really OFF. If the noise stops it's probably an electrical, motor, or loose part problem. If the noise continues for a while, then stops, there may be a refrigerant charge, icing, or TEV problem.
• Check the voltage supply and check for variations in the voltage supply level.

Buzzing & Other Noises at Inverter Type AC Equipment

Things to look for when the AC is buzzing or vibrating

Where to look for causes of inverter u it buzzing when electrical power is off:

No insects, right? NO animals or animal nest, right?

Even if we had an odd problem such as a late-releasing torqued motor component, refrigerant, relief valve, or fan motor, the sound ought to occur once, not repeatedly.

And refrigerant doesn't keep flowing through pipes when a unit is off. Certainly not several times an hour.

• Wind over loose components?
• Sound from other nearby sources?

I would look for:

1. Low refrigerant charge or a refrigerant metering device (TEV thermostatic expansion valve) problem causing freeze-up of the system; later thaw-out might be permitting some refrigerant flow.
   
   (The TEV will usually be inside at the cooling coil).
2. Confirm that the noise occurs when power is OFF to the compressor motor.
   
   That ought to eliminate a failing compresor motor and also loose condenser unit parts such as a grille, motor or unit isolation feet, mounting, piping supports, failing contactor relays, bad fan motor, or other loose parts.
   
   That should also eliminate noises traced to improper voltage such as too-low voltage and a motor unable to start.
3. Try covering the unit or cooling it off with fine spray from a garden hose, simulating rain on the unit.
   
   Does cooling the system change the noise? Inspect the electrical wiring to the unit including the condition of the outdoor service switch, circuit breaker, wiring for a bad buzzing connection - an unsafe electrical fire hazard.
4. If your unit is a heat pump then check the solenoid coil switch that operates the reversing valve on your system - really ask your service tech to make these checks. For some heat pump systems the reversing valve solenoid may buzz for a time when the system stops operating - pressures are equalizing. It's normal.

Please see BUZZING sounds from A/C or heat pump and keep me posted.

Bang noises at VFD / Inverter Drive HVAC Equipment

Definition of VFD or variable-frequency-drive or inverter drive motors & their use in HVAC equipment

An inverter drive air conditioner system uses a variable-speed electronically controlled motor or motors: synonyms: inverter drive, pulse motor, variable frequency drive or VFD.

VFD motors are also called adjustable-frequency drive, variable speed drive, AC drive, micro drive and adjustable speed drive motor systems. These motors use an electronic variable frequency controller to vary motor speed and in some designs to vary motor torque.

When diagnosing a buzzing noise in an A/C unit, including mini-splits and inverter motor systems I'd try to track down the noisy component by inspection and ear or perhaps a mechanic's stethoscope. For example a bad relay will buzz horribly but the repair is much less onerous than a motor that's failing.

However when you see the energy consumption rise, and thinking rather generally, after ruling out intermittent shorts and bad wiring, I do suspect a failing motor or fan bearing. I'm not expert on this but I speculate that any binding moving parts can increase the current draw in an electric motor.

• The most extensive Pioneer service manual I've found is at
  
  http://split61.ru/wp-content/uploads/2013/07/pioneer_service.pdf where you can download your own copy at no fee.

Noise complaints are not a surprise and in fact inverter type HVAC equipment manuals for some Carrier and other brand equipment has a "silence" feature: quoting:

8.4.16 Silence operation(optional) Press the “silence” button on remote controller to initiate SILENCE function.

When the Silence function is activated, the compressor running frequency will keep lower than F2 and the indoor unit will bring faint breeze, which will reduce the noise to the lowest level and create a quiet and comfortable room for you.

Much HVAC inverter repair material discusses troubleshooting VFDs and notes some common defects. Some of these can result in impalanced motor operation and vibration noise.

• MANUALS & PARTS GUIDES - HVAC - Inverter Type HVAC repair manuals for Carrier, Pioneer, Sanyo, Fujitsu and most other brands can be found and downloaded free from this page.
• BLOWER FAN OPERATION & TESTING FAQs-4 - includes Q&As on variable speed motors in general (fans)
• HVAC NOISE-2 CHATTER CHIRP CLANK FAN GROAN - discusses a question of noisy variable speed equipment diagnosis.
• WATER PUMP VARIABLE FREQUENCY / VARIABLE SPEED DRIVE (VFDs) - variable frequency drive water pumps

Sorry I can't offer a smarter guess. Please do keep me informed as what you learn will certainly help other readers.

More general information about inverter-duty motors

Watch out: The US DOE warns engineers and designers about VFDs:

Electronic adjustable speed drives, known as variable frequency drives (VFD), used to be marketed as “usable with any standard motor.” However, premature failures of motor insulation systems began to occur as fast-switching, pulse-width-modulated (PWM) VFDs were introduced.

The switching rates of modern power semiconductors can lead to voltage overshoots. These voltage spikes can rapidly damage a motor’s insulation system, resulting in premature motor failure. - U.S. DOE Motor Systems Tip Sheet #14 cited below

• US DOE WHEN SHOULD INVERTER-DUTY MOTORS BE SPECIFIED? [PDF] U.S. Department of Energy, Advanced Manufacturing Office, Motor Systems Tip Sheet #14, retrieved 2017/11/17, original source: http://energy.gov/sites/prod/files/2014/04/f15/motor_tip_sheet14.pdf

Continue Reading more Noise Descriptions at noise group 2 beginning with CLANKS CLUNKS from air conditioner or heat pump system

...

...

Continue reading at HVAC NOISE-2 CHATTER CHIRP CLANK FAN GROAN - chattering, clanks, clunks, cyclical, fan, groans, growls, honking or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see HVAC SYSTEM NOISE DIAGNOSIS FAQs - index to HVAC noise description & troubleshooting questions and answers about noise in heating, air conditioning, or venting systems.

Or see these

Recommended Articles

• NOISES, HVAC SYSTEM DIAGNOSIS - home
• NOISES, HVAC SOUND DESCRIPTIONS - Index to all noises & sounds
• NOISES, HVAC SOUND RECORDINGS - recordings & video examples of HVAC system noises
• HVAC NOISE-1 BANG BUZZ VIBRATE - banging, bearings, buzzing, thumping, vibrating sounds
• HVAC NOISE-2 CHATTER CHIRP CLANK FAN GROAN - chatter, clank, click, clunk, cyclical sounds, fan noise, groan, growl, gurgle sounds
• HVAC NOISE-3 HISS HOWL HUFF HUM - hiss, howl, huff, hum, groan, woo wuu wuff or humming noises
• HVAC NOISE-4 POP, RATTLE, ROAR, RUMBLE - loud start, popping, rattling, roaring, rumbling, running water sounds
• HVAC NOISE-5 SCREAM SING TRUMPET WHINE WUWU - scream, sing, squeal, trumpet, water sounds, whine, whoosh, whistle, wuwuwu, noises, or flat silence

Or see this

List of Common HVAC Failures that Cause Noises

• BURNED-OUT COMPRESSOR
• CAPACITORS for HARD STARTING MOTORS
• CONTACTOR RELAY DIAGNOSIS & REPAIR
• CONTROL CIRCUIT BOARD, A/C
• COPELAND ELECTRICAL HANDBOOK [PDF]
• CRANKCASE HEATERS
• FAN, COMPRESSOR / CONDENSER UNIT
• FAN NOISES HVAC
• HARD STARTING COMPRESSOR MOTORS

Suggested citation for this web page

NOISES, HVAC SOUND DESCRIPTIONS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

Or see this

INDEX to RELATED ARTICLES: ARTICLE I NDEX to BUILDING NOISE DIAGNOSIS

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