Air Conditioner Noise: What It Means & How to Fix It

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Last updated: 
March 10, 2024

Where in your HVAC unit is the noise coming from?

The first step to solving a problem, any problem, is to identify its root cause – and this simple principle of life definitely applies when dealing with air conditioner noise, too. For this reason, we’ve listed the most commonly encountered sources of the annoying and potentially concerning sounds you’re dealing with.

  • The ductwork. Ductwork noises are at once one of the most common type of A/C unit noises, but they’re also some of the most difficult to pinpoint, track down, and ultimately fix. Some airc conditioning noises can originate from a source that has absolutely nothing to do with your equipment, but is simply being relayed to your home via the ducts themselves. In case you think the sounds are coming in from the ducts themselves, you can look into having vibration dampeners installed onto your HVAC unit.
  • Blower noises. Some so called ‘blower’ noises originate in what HVAC technicians usually refer to as the indoor air handler. That means that your indoor blower, i.e. cooling system.
  • Split system wall-mounted AC units. Fujitsu, one of the world’s best renowned HVAC system manufacturers has some recommendations for handling noises that come from inside split A/C systems mounted on one of the walls of your home. Their main point is that some such noises are absolutely normal and should cause any concern.

For instance, it’s absolutely normal to hear water flowing into the pipes of A/C unit, both while it’s on, as well as immediately after you shut it down. Also, since the front cover of the unit slightly expands and contracts while the unit is on, you may occasionally hear a minute squeak. The same goes for a muted sizzle, which is produced by the unit’s automatic defrosting system. Other sounds, such as bubbling or clicking may indicate actual faults in the system, such as AC refrigerant leaks, or problems with your thermostat. It’s important to have a trained HVAC professional diagnose these problems: self-diagnosis and ‘treatment’ is not recommended when it comes to AC systems, be they split system and wall-mounted or not.

  • Outdoor AC unit noises. These are tricky, because such air conditioner noise is usually indicative of a serious problem, which, in turn, will require a costly repair. Safety first: you are best advised not to open the unit’s front or side panels yourself. If you choose to do so, then at least disconnect the unit from the power supply, since the fans inside these units have been known to chop off unsuspecting homeowner’s fingers.

These are the most frequent causes of air conditioner noise and most HVAC technicians will go on endlessly hairsplitting them into various categories, such as clicks, whirrs, bubbling noises, and so on. While we advise you to always contact a pro when dealing with worrisome sounds which you cannot immediately identify, we will list some of the most usual noises that originate in the air handler section and the ductwork of your AC unit. Take the list below as non-exhaustive and binding in any way, but do use it as guideline for an initial diagnostic of your problem.

Ductwork air leaks

Air Conditioner Noise: What It Means & How to Fix ItThese will usually cause the ducts to roar or hiss. At this point in trying to identify the problem at hand, there are two options:

  1. Your duct connections are causing air to leak out of the system and need to be replaced;
  2. You may want to purchase vibration dampeners, in order to soundproof your ductwork (this is also applicable for furnace ducts, too). These devices need to be installed by professional HVAC technicians.

Bangs or clanks

If you’re keen on home improvement and are also reasonably sure that the banging noise coming from inside your AC unit does not point to a serious issue, you can choose to encase it in paneling or simply deflect the noise, by fencing one of its sides. Experiment with this and find out which variant is best at reducing the noise – or simply choose to purchase a newer AC unit, since such problems are usually caused by older, outdated, low efficiency A/C units. The alternative is that the banging and/or clanking is noise coming from your compressor condenser – a problem that needs to be addressed by a certified professional.

Buzzing and/or crackling

This is usually a problem caused by electric wiring and elements, such as relay switches and other electrical connectors. It’s best not to leave such problems unattended, since arcing at circuit breakers are major fire hazards down the line.

Clicking (or rumbling, rattling, clunking) noises

If this type of air conditioner noise is heard at startup, it usually means that some piece of the hardware has become loose. Check your fan to see if it has come loose or bent and is now hitting against some obstruction.

Duct noises

They can come in under the form of hisses, whistles, roars, clunks, or clanks from the ductwork, as it expands and contracts. It may be the case that some internal noises, such as those caused by a fan, are being relayed by the ducts or that the noises are originating in a completely different location, which has nothing to do with your AC unit. Finally, check to see if there are no small animals trapped inside your ductwork because this, too, can cause annoying noises.

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