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Why Does My AC Make Noise When It’s Off?

Ac Noise

It is normal for the AC unit to make a bit of noise when running. But when you turn it off, you wouldn’t expect the sound to persist. So ideally, your AC should not make any noise when it’s off.

Hearing noises, whether it’s from the indoor unit or the outdoor unit, indicates a malfunction. So, why would an AC unit make noise when it’s off?


Understanding why an AC unit makes noise when off depends on where it comes from. Also, the type of noise it produces gives an insight into what the issue might be.

Some common reasons an AC unit makes noise when it off includes the following:

  • Frozen unit,
  • Loose parts,
  • Condenser fan issue,
  • Electrical issues.

Some AC takes a few seconds to turn off completely. So, when it’s turned off, it is customary to hear a low humming sound. But if the sound is loud, it could indicate something is faulty.

This article discusses why an AC unit makes noise when it’s off. We will also talk a bit about some common types of noise an AC unit may make when off.

4 Reasons Your AC Makes Noise When It’s Off

No one appreciates a noisy machine, including your neighbor. So, if your AC unit makes a lot of noise, you could violate the noise policy.

According to the Environmental Protection (Noise) Policy act of 2007, any appliance you use at home is not greater than 52 dB between 7 am and 10 pm or 45 dB between 10 pm and 7 am.

If your AC unit makes sound noises when it’s off, below are some common culprits responsible for the noise:

1. Frozen Unit

Ac Frozen Unit

For people that live in frigid environments, it’s common to deal with a frozen AC unit. This is because when the AC stays cold for an extended period, it tends to freeze on the inside.

When your AC unit is frozen, it produces a buzzing noise when you turn it on. The best solution to this is to thaw the frozen unit.

There are many tricks you can use to thaw the AC unit. You can commonly use heat from a hair dryer on the exterior to remove the frost.

Alternatively, turn the fan on or leave the unit off until it defrosts.

2. Loose Parts

Ac Loose Parts

When there are loose parts in the AC, it can be the culprit behind the noise your AC is making. The AC is made of many parts, so it’s easy for a screw or fastener to lose.

Dealing with loose parts on your AC unit may seem like no big deal, but it could lead to more significant problems when those parts come loose completely.

As such, when you turn off your AC and you hear a banging or clanking noise when it comes to a halt, it indicates some components have come loose.

Ideally, to fix this, remove the front panel of the AC and access the unit. Check the screw and integrity of each component to find the culprit.

3. Condenser Fan Issue

Condenser Fan Issue

The condenser is a critical part of any AC unit. The condenser is the part of the outdoor unit that releases or collects heat, depending on the AC unit.

The condenser uses coolants and a fan to work effectively. If the condenser fan develops an issue, it will likely make a lot of noise when the unit is turned off.

You will hear a loud buzz when the condenser fan has developed an issue. The issue can come in so many forms.

Sometimes, it could be that the fan’s fin is broken or the fan motor has blown out. Whatever the case, you may need to replace the fan to solve the issue.

4. Electrical Issues

Electrical Issues

Another issue that can be responsible for the noise coming out from your AC unit is when it has an electrical problem. For example, the contactor relay switch is a common problem you will experience with most older AC units.

The AC unit will buzz when the relay switch interacts with the thermostat to regulate cooling.

When this low-voltage switch fails, it will continue to make a buzzing noise regardless of whether the unit is working on not.

You should unplug the AC unit from the power outlet in such cases. In addition, electrical arching or shorts can result in fire hazards.


When you turn off your AC unit, and it makes a loud noise, it signals something is wrong. However, it would help if you did not panic immediately when you hear the buzzing noise.

Instead, know that your AC unit will need a maintenance service sooner than you might have anticipated.

Frequently Asked Questions

What Should You Do When You Hear Strange Noises From Your AC?

When you hear strange noises from your AC, you first want to turn it off and unplug it from the power source.

Next, you should call the AC repair company for a maintenance service.

What Type of Noise Is a Bad Sign From My AC?

Not all noise from your AC is a sign of something bad. For example, a humming noise is normal. But when you hear the following noise, it can be negative:

  • Buzzing
  • Rattling
  • Clicking or banking
  • Pulsating

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