Get Annoyed by Air Conditioner Making Noise When Off

Imagine if you are in a hurry to catch the bus, but your air conditioner is making noise when off – either knocking or gurgling noises. It’s quite annoying.

Before calling professional repair services, you should better identify the most common component malfunctions to have caused the noises.

AC Making ‘Knocking’ Noise When Off

There are many reasons why your AC makes a loud bang when being shut off. The problems can come from inside and outside.

Air Conditioner Making Noise When Off

If it comes from inside:

  • Too dirty or restrictive air filter slamming against the return grille. The filter drops onto the grille, causing your air conditioner making knocking noise when off.
  • Contracting or expanding ductwork caused by pressure and temperature changes. A certain amount of popping sound is considered normal, but when it gets louder and more frequent, you should better call a technician for an advanced check.
  • An issue with the air handler caused the blower wheel to bang against other components.
  • Closing of dampers installed in the ductwork to direct air to certain rooms. If the noise is getting worse, you should invite a technician to make sure it’s installed correctly.

If it comes from outside:

  • Outdoor unit fans become loose and need to be repaired or replaced due to general wear and tear.
  • An unbalanced compressor’s support springs cause the refrigerant pump to bang against the case.

AC Making ‘Gurgling’ Noise When Off

Have you ever heard your AC making a disturbing gurgling noise that occurs when it turns off? It is more likely caused by condensation (water) residue in the P-Trap.

P-Trap? What is it? It is a part located in the evaporator drain pan, attached to the discharge outlet, and used to condensate water, so it will not be sucked back into the air handler when your AC is operating.

When your AC is on, the fan will start running. This will create a vacuum within the air fan chamber. However, when the AC is shut off, the negative pressure in the room will turn positive, resulting in a pressure differential and likely producing unusual noise. Freeing the drain pan, P-Trap, and condensate drain from any obstructions is suggested to diminish the noise.

In addition, the extraneous noise may also come from the freon leakage. Freon is a gas that changes its aggregate state very fast. It turns from a gas into a liquid and back again. When the AC is operating, the compressor will accelerate the freon in the system, while it will slow down after switching off. The noise is usually heard for 5-10 minutes and is considered normal in the operation of inverter air conditioners.

Specifically, due to the temperature differential between indoors and outdoors during winter, the gas cools and is pushed out by a liquid whose density is higher. This kind of movement may lead to gurgling noise.


If you noticed a buzzing noise and clicking noise coming from your air conditioning unit, along with a loud noise coming from the blower fan and upon further inspection, you found a refrigerant leak, loose parts, and an electrical problem that was affecting the blower motor and outdoor fan. Moreover, if you find the fan blades of the condenser fan motor were dirty, which was contributing to the AC noises. Overall, it was clear that the air conditioning system was in need of significant repairs.

After acknowledging the causes of the air conditioner making noise when off, you can either attempt to fix any problems by yourself or call professional repair services.

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AirconMag is an experienced author and Air Conditioner expert. With years of practical experience in the field authored several informative articles on various aspects of AC unit, including installation, maintenance, and repair