You’re probably familiar with the typical sounds of an air conditioner that’s running properly: the gentle hum of the fan and the blowing of air through your ductwork and vents. But if those sounds are replaced by banging, hissing, grinding, or any other harsh noises, there’s probably something going wrong with your system. Today we’re going to talk about why your air conditioner might be making noise and how to interpret what those noises mean!

Air conditioner’s outdoor unit making noise

Let’s start with your air conditioner’s outdoor unit. If you hear a sudden loud banging or rattling, it’s possible that a twig or some other kind of debris fell into the unit and was hit by the fan inside. If you can see the debris, shut the power off to your unit and remove it. If not, contact Jerry Kelly Heating & Air Conditioning so that we can get inside the unit and remove the debris before it causes any damage.

Another sound you might hear from your outdoor unit is a buzzing noise. This is often the sign of an electrical issue with one of your unit’s components like the contactor. Electrical issues should only be handled by a trained professional.

Finally, if you hear a hissing noise near the copper tubing coming from your outdoor unit, you might have a refrigerant leak. This should be taken care of by Jerry Kelly Heating & Air Conditioning as soon as possible because it will force your air conditioner to operate inefficiently and is bad for the environment.

Air conditioner’s indoor unit making noise

Now let’s turn to the indoor portion of your air conditioner. If you hear a loud grinding sound inside your home, there could be a problem (such as lack of lubrication) with your air conditioner’s motor or one of its moving parts. This should be taken care of by a professional.

If you hear a rattling sound from your air conditioner, your unit likely has a loose screw or belt that is allowing some of its parts to move around and rattle against each other. Contact Jerry Kelly Heating & Air Conditioning so that we can inspect your unit and tighten any loose parts.

Finally, a hissing sound can also be heard from inside your home. If the hissing sounds like it’s coming from inside your vents, you likely leak somewhere in your ductwork that will need to be sealed up.

You expect your furnace to heat your home – not make noise. So, if it does make strange noises, it’s important to know whether they are ‘normal’ or ‘not normal’.


– The nice quiet hum of motors running and fans blowing and air whooshing through vents all fall under ‘normal’ and we expect our mechanical furnaces to produce them.


– Popping noises are also pretty normal. The first few times you use your furnace especially, you may notice popping sounds when the furnace kicks on and kicks off. This is the sheet metal in your ductwork responding to the pressure of heated air – popping in as a reaction to the negative air pressure of the fan blowing in heated air and popping back out when the fans shut off and pressure is released.


– You might hear a rattling noise if the fasteners to the metal housing of your furnace have worked their way loose. This isn’t anything serious and can easily be fixed by tightening the fasteners. You might also hear a rattling noise if some piece of debris has become trapped inside your unit, clanking around and possibly causing damage to the fan or motor. If the rattling noise comes from inside your unit, it’s best to shut it off and call a furnace technician.


– If you hear a rhythmic thumping, you likely have something out of balance, like a blower wheel. This could cause significant problems for the mechanical operation of your furnace. Have it inspected to avoid a potential safety hazard.


– A low rumble is normal when a gas or oil-fired furnace first kicks on. However, if that rumble grows loud or lasts too long, it could indicate a serious problem with your burner. In this situation, it’s advisable to turn off the furnace and call for service to avoid a potential safety hazard.


– A scraping noise coming from your furnace is never a good thing. It usually means a fan blade is scraping up against something it shouldn’t – that means it’s out of kilter and not doing a proper job of facilitating proper air flow. This could lead to a motor blow out. So if you hear scraping – call for help to have it inspected to make sure it’s not something that will lead to motor burnout.


– Hissing sounds are caused by something escaping. Hissing could mean there’s escaping air due to an improperly installed air filter, or one that is the wrong size. Hissing can also mean there are too many closed vents, or a leak in your ducts.


– A person who is whistling is probably in a good mood – but HVAC equipment that is whistling is NOT happy. It could be an indication there’s a refrigerant leak in your condenser, or some other thing that’s causing a build-up of internal pressure. This is a ‘not normal’ noise and if you hear it, whistle for a service technician.

Avoid air conditioner noises with annual tune ups

Almost all of the problems that we listed above can be avoided by scheduling an annual tune-up with Jerry Kelly Heating & Air Conditioning. During your tune-up, we’ll check every one of your air conditioner’s components and ensure that it is running properly and noise-free.

If you have any questions about why your air conditioner is making noise, or if you’d like a cooling system serviced or installed in your home, contact [companmy_name], your St. Charles air conditioning contractor. We service the St. Louis area, including towns like Clarkson Valley, Clayton, and Cottleville.

photo credit: Quinn.Anya via photopin cc

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