During times of high air conditioner usage, you’re probably going to hear some noise.
Most AC noises are perfectly normal: the sound of the outdoor unit turning on, the soft movement of air through the ducts… nothing to worry about there.

But then there are those “other” noises. The kinds that make you ask, “Why is my AC making noise – and why is it so darn loud?”

Let’s consider a few of the more troublesome air conditioner noises you might be hearing. In most cases, these are the ones that require professional assistance. We’ll start with humming or buzzing noises and move on to rattling or chattering noises.

Why is my AC making a humming noise?

Whether it’s a new humming noise or just a louder hum than the AC was making previously, you might be wondering why your AC sounds the way it does. Unfortunately, a humming noise could indicate that something is wrong with the unit.

Oil leak

A loud humming noise could mean that the AC is losing oil. If there isn’t enough oil in the system, the compressor will be insufficiently lubricated. When this is the case, it will run louder than usual… until it eventually fails.

Call an HVAC pro to inspect the unit. If you’ve got an oil leak, you may not have long to wait until a vaguely annoying humming noise turns into a bigger problem.

Refrigerant leak

Refrigerant leaks can also cause the compressor to operate at a louder volume. That’s because the compressor probably is operating at a higher temperature than normal, causing it to make more noise.

When you’ve got a refrigerant leak, you may also notice that the compressor isn’t the only thing operating at a higher temperature. Your home will probably be a whole lot hotter as well! Having the right amount of refrigerant is essential for proper AC operation. If you’ve got a leak, the system may struggle to keep up.

Dead capacitor

If the outdoor unit hums but won’t actually start up, one of the capacitors probably failed. An HVAC technician can change out the capacitor and have you back up and running right away.

Dirty outdoor coil

When was the last time you called an HVAC technician to clean your system’s outdoor coil? If it’s been awhile and you’re hearing a new humming noise from the AC, it might be due to a really dirty coil.

Any time your AC’s coil is coated in dust, dirt, and grime, it will struggle to transfer heat to the ambient environment. One of the many downsides to this scenario (aside from a drastic reduction in AC performance) is that the dirty coil drives up the head pressure in the unit, which heats up the compressor.

And as we saw in our refrigerant leak example from above, a hotter compressor is a louder compressor.

The good news? Having a dirty outdoor coil is 100% optional. Homeowners who sign up for PV Priority Service get two system tune-ups and inspections per year. Before the cooling season, this tune-up includes a comprehensive cleaning of the outdoor coil. That way, you never have to worry about it getting so dirty that the AC can’t do its job.


Sometimes, we’ll get a call from someone asking, “Why is my AC making a buzzing noise?” We’ll check on all the stuff mentioned above, but we won’t find any problems. What usually is the case, however, is that the AC is really old.

Just like a vintage car with a well-worn motor, an old air conditioner might be louder because it’s, well, old.

If the noise is bothering you, you can always consider getting a new air conditioner. Manufacturers have come a long way in recent years toward reducing the noise generated by air conditioner compressors. Besides, replacing an old AC before it breaks down in the middle of July is usually a smart decision.

Why is my AC making a rattling noise?

If it sounds like something is rattling around in your air conditioner, that might be because… something is rattling around in your AC! Seriously, it happens.

But it could also be something else. Let’s look at the most common sources of AC rattling noise.

Loose screws

From time to time, we encounter air conditioners that haven’t been serviced in many years. Besides all of the things that can go wrong if your AC isn’t properly serviced, many of these units have loose screws either within the unit or outside on the system housing.

If nobody has unscrewed anything to service the unit, vibrations from the AC itself can loosen the screws, causing them to rattle!

Whenever we encounter this, we just tighten the screws. Well, we also service the unit – that part is super important – but we tighten the screws completely before we leave the scene. The result? No more rattling.

Bad contactor

This one is usually more of a chattering noise than a rattling noise. Your AC’s contactor helps power major components in the outdoor unit, such as the condenser fan and compressor. When it starts to die, it might make really worrisome chattering noises.

The bad news is that your AC won’t run without a working contactor. If yours starts making noise, it’s probably just a matter of time before it dies. The good news is that an HVAC technician can easily replace the contactor and get you back up and running.

Your AC is probably making noise for a reason

And you should probably have it checked out! Any time you’re asking, “Why is my AC making noise?” there’s a good chance you’ve got a problem that needs to be solved quickly.

If you live in Metro Atlanta and are concerned about a noisy air conditioner, PV can help! Give us a call at (404) 994-2229 today or fill out the contact form below.

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