5 HVAC System Sounds You Don't Want to Hear

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Chandler AC Repair

Subject: AC Tune-up

Glad I came across this post, good information and very explanatory. Don't forget to regularly schedule your Glad I came across this post, good information and very explanatory. Don't forget to regularly schedule your AC and heater tune-up to avoid costly repairs


Subject: HVAC unit making banging noise when the system stops

My tenant has been complaining that she hears banging (two metal pieces) noise from the HVAC system in the attic...she sleeps in the first floor and the attic is above the second floor. This soundswakes her up in the night; she does not hear this noise during the day.

An A/C mechanic was there to check it out but he did not see any problems. So little confusing as to what could be causing this noise.

Priscilla Wakefield

Subject: Buzzing from outside air conditioner unit

I am hearing what I can only describe as a motorized buzzing sound coming from the outside unit also not blowing out of the registers as strong as it used to and not able to keep house cool during the day at night it blows strong and house becomes comfortable again. What could be the problem?


Subject: Buzzing

Not being able to look at the "outside" condenser unit I would say that the relay contacts aren't making good contact and are arcing, I.E. they have corrosion on the contacts. If you live where there are fire ants, then that is probably your issue. Fire ants love the "taste " of A/C electrical contacts. This is the same response that I gave below. But it could also be that the condenser fan is not turning which may be that the start capacitor or fan is bad.


Subject: Low concussion rumbling in window unit.

I was in bed the other night and I swore there was a sound that freaked me out (didn't help that I watched Ghost Asylum before bed) The sound seemed to be coming from downstairs (I sleep on the second floor) sounded like very low thunder from off in the distance. It shakes my whole wall.


Subject: zapping noise

Not being able to look at the "outside" condenser unit I would say that the relay contacts aren't making good contact and are arcing, I.E. they have corrosion on the contacts. If you live where there are fire ants, then that is probably your issue. Fire ants love the "taste " of A/C electrical contacts.

Laraine Boyles

Subject: loud raspy noise

At beginning just as burner comes on and just when burner goes off. Not in sync with blower on and off. Accurate man was here one hour and it did not make noise. It is getting longer and louder all the time, but I can't say it will do it all the time. I think maybe when colder then again it will go awhile without noise.

Brooks Nguyen

Subject: Hvac under the house humming

My heating and air is electriic . I have an goodman unit but under my house it hummings and makes me think something is wrong . I know my emergency heating strips are out because the hvac man told me . Could that be the problem ?


Subject: Recently has the first real

Recently has the first real cold weather of the season came on we awoke to what I called a droning sound in the house. After investigating some it was realized that it was the Central Heat. Every time the heat kicked on (and it was working) we would hear the noise almost has if it was coming through the vents. We have a American Standard gas outdoor system about 8 years old without any previous problems. It was looked at the next day and supposedly fixed, but the sound persisted for another day until it simply stopped. No sound, No heat. This time the repairman quickly diagnoised that it was a bad inducer motor. Apparently the teeth of that motor fan had rusted off until none were left and thus the system wouldn't ignite. New inducer motor was about $750.


Subject: Whomp, whomp sound from inside compressor unit

Over the last number of days my compressor started making this womp womp noise that lasted longer and occurred faster and got louder over the last two days. Also compressor and the heat pump outside were increasingly disconnected with starting and stopping in no relation to each other. Naturally I called them first thing this morning as I am under a service contract. Technician arrived at noon and said that my blower was going bad and with that it quit entirely. new blower was put in this afternoon and my house is cool and everything sounds normal again. Unit is 3 years old. I clean the filter and flush the drain line once a month. First thing I did was flush the drain line. but after reading comments I'm going to go and check the filter.


Subject: knocking sound

I had my house built in 2004 and from 2004 to 2013 we replaced 8 compressors due to various problems they were under part warranty but still cost supply and labor 500.00 each. Ouch! We called. A friend from church who owns a/c co and replaced outside unit and inside unit several thousand dollats in Late 2013 now I'm up at three a/m it's three am and the outside unit is making a knocking noise (loud) I'm just outside warranty could it be compressor again ? I live in Tampa fl. And a/c well it's a must have or die and I have.a 2 and 4 yr old I'm so frustrated help me

Brian Nagle

Subject: Equipment making unusual noises

Equipment making strange noises. Keep your equipment under a service contract. Be sure the service calls are covered all season long. If replacement equipment is needed, it is completed sooner and your equipment is checked so there is not premature wear. Think of your investment like a new car. You would not drive for 20000 miles without an oil change. Be smart, not penny wise.


Subject: Noise when Air comes on

I have a new Lennox unit. Noise when starting sounds like door slamming or something heavy dropping. Sounds like it's coming from compressor. Air company that sold and installed unit has been here twice and thinks it's fine. Don't think they heard it - don't want (whatever it is) to hurt unit and go out when service isn't covered anymore.

eric rasmussen

Subject: Lennox elite 14 loud sound like door slamming on startup

I had the same symptoms and had the tech out to repair, he installed a hard start kit which had no effect on the noise. I was told sometimes it takes a while to break in before quieting down. A month ago the hard start kit exploded and the tech came out and said trane and lennox have a lot of these problems and clearly I got a lemon. I have had 3 estimates from the dealer to replace a compressor 1150.00 next day 750.00 next day a message saying maybe and additional discount off the 750.00.
I would make them fix it or replace it if I were you before you hit 12 months or you will be up a creek like me with a two year old unit that I have NO faith in and I am afraid repairing it will be throwing good money after bad.


Subject: Pigeon Sounds. But no Pigeons.

I was sitting in the room right infront, I I heard what soundsled like pigeons. I live in the country, so no pigeons. There aren't even pigeons, much less any birds here. But the sound wasnt comeing from the fan. Cause we turned the fan on and no noise. But then we turned the whole thing off and a few mintues later the thing started to make the sound again. Now its making a long hum sounds. That sometimes sounds like sound like the sounds off of a morse that is high pitch. What could it be?


Subject: Ac unit

When our ac first turns on I hear what sounds like fan blades hitting , for about five to 10 sec. Then goes away . From the inside portion of the ac system . System is about 7 yrs old. Inside the house portion of the system not the outside ac itself


Subject: Knocking Sounds

I have recently noticed knocking sounds when the outside unit shuts off as house reaches set temperature. Does not occur at all times and seems to happen when thermostat is set low at 72. What is the cause of this?

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what should you pay.  You pay what you can afford.  1100sqft unit requires a min. of a two ton unit.  prices range from 2100-2900 depending upon the seers of the system.  13 seer is the min. the law requires  and for your situation with 1100 sqft.  do not worry about the seers as long as it is to code.  the bigger the house the more seers for economy.  1100 sqft is at the border line for a two ton system.  It is more important to have your new system balance, there is where you get the economy on your electric bill and gas.  Bryant, lenox, ruud and carrier are the brands you should stay with.All have the same basic factory warrantee and will last you longer than you expect as long as you maintain it with regular check ups twice a year once in the spring and then in the fall.

raymond gonzalez
koolray heating and air

APRStore.com offers a nice sizing chart for HVAC capacitors and furnace capacitors. Most of the capacitors I've looked at are $5 to $15 dollars, so a little less than Home Depot and Lowes.


Replacement is really easy, but be sure to watch a youtube video on how to replace it like this one: https://www.youtube.com/watch?v=_IpydZIsOJg


Stay safe and hire a professional if you feel unsure about doing it yourself!

The only thing of importance, is the hvac professional you choose to use. Alot of manufacturer's pieces are built relatively the same, and will last about the same amount of time. The thing that matters most is what you can not compare between companies, and that is the installation. Purchasing a system is not like purchasing a car, where no matter where you buy it, they are all the same. Each installation is different, and usually what you are paying for is the level of expertise, and quality of the installation, the company who will actual give you the warranty, and the comfort that you will receive. Manufacturers warranties disappear every day. They always have a loophole where they can get out of paying, but your local dealer wants to keep you happy for future work, and to protect his reputation in the communiy. Look up 4 year old Nordyne and Goodman warranty problems. Choose the HVAC professional first. It will cost you the least in the long run. I have had to totally redo plenty of installations that were just performed because of an uncomfortable customer, and a system that keeps breaking down. The equipment is only as good as it's installation, and over 70% are not installed correctly.
I think maybe you are confusing SEER, which is an efficiency-related rating (higher SEER means more effective use of the electric power used to compress the gas), and TONS rating, which is a measure of the total cooling power of the system. (Tons used to mean how many tons per hour of ice was used in evaporative cooling building systems - a Refrigeration or Cooling Ton equals 12,000 Btu/Hour of energy exchange. A BTU, which is another antique measure but still used, is the energy needed to change the temperature of a pound of water one degree fahrenheit. Unfortunately, because of varying humidity and evaporation, this is not readily related to house air heating or cooling without a lot of assumptions and some computations. Relating this to today's world - the Manuals BayAreaAc referred to account for all these energy conversions and determine an estimated cooling (or heating) requirement for your specific house. The type of construction, solar exposure, general climatic conditions such as average temperatures, humidity, and hottest and coldest normal ambient temperatures and desired inside temperture are all taken into account in the more sophisticated versions of the analysis, so there is no "standard", though a rough old rule of thumb was about 1 ton of cooling per 500SF of house. Obviously, this was a WAG only because it did not account for insulation, type of roofing, whether you live in Alaska or Miami, etc. The ACCA manuals do a very simplified form of evaluation to arrive at a "design", which generally will be adequate. OF course, highly precise calculations are not really needed because A/C units generally come in even ton ratings - so if you are at say 2.6 ton requirement you will be getting a 3-ton unit anyway. SEER ratings are not a direct measure of efficiency, but the relative difference between ratings gives you good idea of the unit's relative efficency in using electricity - so a 16 SEER should be about 19% more efficient (so roughly comparable lower electricity bill) than a comparably sized 13 SEER unit. 13 SEER is the lowest efficiency currently allowed to be built for general use, 19 SEER is about the highest efficiency made by pretty much all manufacturers, and about 25 SEER is the highest rated though very pricey shelf-item units, though special construction custom units can reach about 30 SEER. Note however, like any government sponsored rating, much of it is hooey when you get down to it - for instance, SEER ratings are figured based on 80 degree inside air temp and 82 degrees outside, when that is far from the normal case of mid to low seventies inside and high eighties or above outdoors. This makes the absolute SEER rating meaningless, but relative numbers still have meaning in comparing units. Note these efficiency ratings are for conventional air conditoners and heat pumps working in ambient air conditions. Ground sourced Geothermal or lake/river exchange cooling units, though initially more expensive in most cases, can greatly exceed the air-exchange unit efficiencies because they are exchanging heat with cold natural water rather than with a high-temperature outside air, and instead of continually compressing a gas are just circulating cold water. I worked on one geothermal cooling project which had almost infinite efficiency, which of course makes no sense - but the only power was for sensors and a control valve as the water flow was single-pass under gravity flow, so no power was used to circulate the water.