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 several reasons why you might hear a loud bang or knocking noise coming from your air conditioner when it’s turned off. These issues can originate from both the indoor air handler and the outdoor unit.

Air Conditioner Making Noise When Off

If the noise originates from inside, it could be due to:

  • A dirty or restrictive air filter slams against the return grille, causing a knocking noise when the air conditioner is off.
  • Ductwork contracting or expanding due to pressure and temperature changes. While some popping sounds are normal, excessive noise may require a technician’s evaluation.
  • A malfunction in the indoor air handler, where the blower wheel may be striking other components.
  • Improperly functioning dampers in the ductwork can exacerbate the noise. A technician’s inspection can ensure correct installation and operation.

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.

Read also: Air Conditioner Drain Line Outside House Leaking Water

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.

Read also: What Is a Dual Inverter Air Conditioner

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 detect a buzzing or clicking noise, along with a loud noise coming from the blower fan, it could indicate various issues. These might include a refrigerant leak, loose parts, or an electrical connection problem affecting the blower motor and outdoor fan.

Additionally, dirty fan blades on the condenser fan motor can contribute to these noises. In such cases, it’s evident that the air conditioning system, particularly the relay switch and other components, requires thorough 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