What’s Causing Those Weird HVAC Noises (And What to Do About Them)

Your HVAC system is there for one reason: to make your home more comfortable. So, in addition to keeping your home at the desired temperature, your HVAC is designed to operate as silently as possible so it doesn’t disturb you. You shouldn’t even notice it when it comes on.

If you do notice it, then it sounds like you have a problem. Ok, we’re sorry about the really, really bad pun. But it’s true that HVAC noises are a common, and definite, sign that there’s a problem with your system.

If you hear your air conditioner humming inside, clicking, banging, or making any of the other noises on this list, you need to call an HVAC professional fast. A minor problem could take a very expensive turn for the worst if you leave it unfixed.

To help you understand what’s going on with your noisy air conditioner, and how urgent the problem is, read this guide.


1. Banging

What causes that loud banging noise every time your AC comes on? Fortunately, as bad as it sounds, it’s probably only a loose or broken (but non-essential) part. In most cases, it’s a simple fix.

The parts that are usually responsible for banging noises during operation are a loose crankshaft or piston pin, a broken connecting rod, or an unbalanced indoor blower.

However, you should definitely not dismiss a banging noise as “no big deal.” For one thing, there’s no reason you should have to put up with an obnoxious AC system with so easy a fix.

Secondly, there’s still a chance that it might be a big deal. In some cases, a banging noise indicates that your AC compressor needs to be replaced.


2. Clanking

Clanking is often caused by the same issues that cause banging noises, which we described above. A loose or malfunctioning part may have caused the compressor to come loose. Therefore, as with banging noises, you might need to replace the compressor.

Another common cause of clanking is that the fan blade of the indoor blower is out of place. When the fan is warped or off-center/off-track, it knocks into other components every time it spins, causing a repetitive clanging noise. Or, the fan housing could be dented or warped in such a way that it contacts the fan blade during operation.

Obviously, any of these issues are bad news for your HVAC. Operating the fan in this condition could cause further damage to the contacting components or the fan motor. Metal hitting against metal can even cause dangerous heat and sparks—a blatant fire hazard.


3. Clicking

A single clicking noise when your system starts or stops is nothing to worry about. This is a common occurrence in many HVAC systems and does not indicate a problem. It’s the same type of electrical clicking you sometimes hear when you turn on a lightbulb.

On the other hand, constant clicking during operation should not be happening. To diagnose what’s causing it, you’ll have to pay attention to where it’s coming from.


Outside Clicking

If you hear the clicking coming from outside your house, it’s a problem with the outside compressor. It’s probably something as simple as a loose part like a bolt or refrigerant tubing. But a loud clicking could mean a dying capacitor, a very important component of your HVAC.

Either way, you’ll need to have a professional come and take a look at it.

A Clicking Fan

Does the clicking start slow when the system first comes on and then get faster? If so, it’s the fan contacting some other component as it spins, the same as with a clanking noise.

Constant Or Sporadic Clicking Inside the House

If you hear the clicking inside the house, it’s most likely an electrical problem. It could mean that one of the electrical components, like the thermostat or some other control, is malfunctioning.

Or, it could be that some of the systems wires are shorted together. Since wiring issues can be a fire hazard, you should call it in right away.


4. Popping

There’s good news and bad news concerning popping or ticking noises coming from your AC. The good news is, this is nothing serious.

The sound is caused by the metal air ducts expanding and contracting due to temperature changes when hot or cold air circulates through them. This is common in a lot of HVAC systems.

That’s sort of the bad news. This popping sound when you run your system is not going to go away on its own.

Fortunately, there is something you can do: insulate your ducts. Adding more insulation between the duct and the duct hangers may stop this sound entirely. If not, it should at least muffle the noise.

Besides the more insulated your ducts are, the more energy-efficient your HVAC is.


5. Buzzing

Truth be told, a buzzing noise coming from your HVAC is difficult to diagnose without professional help. That is, this noise could indicate a number of different problems, including:

  • An overfilled air filter
  • Loose components
  • Unbalanced or loose fan blades
  • Unbalanced, loose, or malfunctioning blower motor
  • A condenser coil in need of maintenance
  • The copper lines are intertwined or rubbing against something else
  • There is debris in either the outdoor or the indoor unit
  • Refrigerant is leaking, which is freezing up your air conditioning system (if your AC isn’t cooling, this is why)

The short answer is: if you hear your air conditioner buzzing, change your air filter. If the buzzing persists, shut the system down and call a professional to come and look at it.


6. Squealing

Some HVAC units always make a squealing noise upon startup. If this has always occurred with your system, you know it’s nothing to worry about. However, if the squealing is a new occurrence, it indicates a problem.

The sound is most likely coming from the indoor blower motor or the outdoor fan. Sometimes the squealing is caused by other parts malfunctioning, like the blower wheel and housing. But you hear the noise as it is conveyed through the duct system.

If this squealing noise has started only recently, and not just when the system starts, call it in.


7. Humming

Humming, like squealing, may be a normal occurrence of your HVAC operating. All HVAC systems make a quiet hum when running caused by the electricity being used and/or the fan.

Since quietness is a selling point for HVAC systems, some of them run almost silently. But there’s no way to remove the hum completely.

However, if the humming of your AC sounds different than it used to, louder or more like a buzzing or clanking, this indicates a problem. It could be a version of the buzzing or clanking problems we described above.

It could also be that loose parts and/or refrigerant piping are causing vibrations in the system. If that’s the case, it could lead to further system damage rather quickly. Thus, if you hear your air conditioner humming in unusual ways, call an HVAC technician.


8. Rattling

A rattling noise is often a sign that your AC system is in its final days, especially if the system is over 10 years old. Various causes of rattling noises, like loose or damaged parts, are common toward the end of its lifespan.

However, these causes don’t necessarily mean the system is dying, especially if the system isn’t that old. It could just mean that the loose or damaged parts causing the noise need to be fixed.

Another possible cause is that debris in the system, like leaves and twigs, is obstructing its function. You may want to check for debris, damage, and loose screws/bolts in your outdoor system yourself.

If you see any, shut your system off and call it in. Running the system in this condition could cause extensive damage very quickly. Even if you don’t see the cause, call it in regardless.


9. Flapping

A flipping noise is another sound commonly caused by debris in the path of the fan blade. Usually, it’s natural debris like leaves or twigs, even sometimes live vines growing into the outdoor unit. Although, the debris is sometimes litter like plastic wrappers, paper, or fabric that has fallen through the grate and into the system.

If you see any of this and can clear it yourself, do so, especially in the case of live vines. As vines grow, they will wrap around anything they can, clinging and pushing, literally attempting to strangle and tear apart your HVAC.

It’s imperative that you uproot these and remove them from your system. If you cannot do so yourself, call a professional.


10. Whistling

If you hear a loud whistling or screaming noise when your system runs, shut it off immediately and call professional help. Do not turn it on again until a professional checks it.

The reason for this caution is that whistling or screaming could be caused by a refrigerant leak. Refrigerant leaks are highly toxic to any humans or animals living in the house.

Furthermore, the noise could also indicate a dangerous buildup of pressure in your HVAC’s compressor. Often, in this case, your system will shut off automatically to protect you.

A faint whistling, on the other hand, may simply be an airflow problem. Just as you sometimes hear the wind whistling through objects outside, this can occur as air circulates through your air ducts. Typically, this type of whistling indicates dirty, clogged, undersized, or leaky ducts.

Nevertheless, operating an AC that’s whistling is not worth the risk. Shut it down and call an HVAC professional right away.


HVAC Noises

Hopefully, you found some of the answers you were looking for on this list. But, regardless of what’s causing all those HVAC noises, you should always have strange appliance behavior checked by a professional.

To that end, if your system is making any of these noises, click the link at the top of this page to contact us. Also, learn more about our services here.