Why Does My Air Conditioner Make Noise After Shutting Off?

The last thing you want to hear in the middle of a Montgomery, AL heatwave is a loud banging or rattling noise emanating from your air conditioner. It could mean the one thing providing you relief from the sweltering heat is about to go kaput. It might find it especially unusual if you’re hearing this noise if your AC unit isn’t running.  If your HVAC system is making a clanking, clicking, squealing, or hissing sound this could be a warning that there is an underlying problem. You will want to get this air conditioning problem fixed before cool air stops blowing altogether, and your home turns into a sauna. The Hans Heating and Air professionals share some insights on what your air conditioner might be telling you. 

Where Is The Noise Coming From?

There are a few common air conditioner problems that cause unusual sounds other than the normal, low, soft rumble of cold air being blown through the ductwork of your home. It’s easier to zero in on the problem if you can pinpoint where the sound originates. 

If the noise is coming from the inside of your home, the problem may be:

  • Faulty electrical components to the air conditioner’s blower 
  • A dirty air filter that is slamming against the grill of your airflow duct
  • A filter that is not the right size for the air flow duct
  • A return duct that is too small
  • Expanding or contracting ductwork that makes a loud noise like slamming after the air is shut off
  • A problem with the indoor air handler that is causing the blower wheel to slam into other components

If the noise is coming from the outside of your home, the problem may be:

  • Old worn-out support springs inside your AC unit’s compressor are allowing the refrigerant pump to bang into the case of your compressor
  • The compressor’s motor in the outdoor unit might have loose components and is in need of repair or replacement 
  • A failure of the outside AC unit’s relay switch which regulates the voltage going into your home

What Kind of Noise Is It?

Another way to determine the problem with your HVAC system and to understand why the air conditioner making noise after it’s been shut off is to describe the sound itself. Certain sounds can indicate a mechanical error while others can suggest some kind of electrical connection issue. Here are some of the common sounds and their associated problems:


A banging noise coming from your air conditioning system almost always involves loose parts. The indoor blower fan  may have a loose fan blade, or the outside compressor may have a connector rod or pin rattling around inside its metal housing.


A loud noise like a clanking sound can be indicative of an out-of-balance fan blade in the outside compressor or the indoor fan. If the blades are not realigned, the fan can cause damage to the air conditioning system over time, and decrease energy efficiency.


A clicking sound during the cooling cycle of an air conditioner may mean there is a problem with the relay switch or your thermostat is dying and needs to be replaced.


Hissing can be a small problem or a very big one. The small: An air leak in a duct which can be repaired easily with some duct tape. The big problem: A refrigerant leak could force you to have to replace the entire air conditioning unit. 


A high-pitched squealing noise from inside the compressor is a sign of high internal pressure and should be fixed immediately. A less serious cause of squealing could be from a dry fan motor bearing. Just like with any other machine, when metal touches metal, it needs to be lubricated regularly to prevent overheating and other kinds of damage caused by overuse.


If you hear a buzzing noise when your air conditioner is off, it is often indicative of an electrical issue. You’ll want to call a professional for service to inspect your electrical components as electrical problems could cause a fire. 

Hans Can Fix The Problem

The Hans Heating and Air professionals are available 24/7 to help you figure out what’s wrong with your air conditioner and fix it the same day or you don’t pay. Whether it’s replacing a loose rod rattling around in your outside compressor, fixing a buzzing relay switch, or realigning a clanking fan blade, our technicians can help make the noise go away. Talk to the professionals at Hans today to see how we can make your Montgomery, AL home comfortable and quiet.

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