FAQ: Split Systems The indoor unit is making a strange noise.
Most of the noise your air conditioner makes are normal. While an air conditioner is operating as well as immediately after you turn it off, you may hear water running in the pipe. You may hear refrigerant circulate in the air conditioner for 2 to 3 minutes after you turn it on.
While an air conditioner is operating, a slight squeaking noise may occur. This is because the front cover of the air conditioner slightly expands or shrinks due to temperature change.
During heating operation, a sizzling noise may be heard occasionally. This is produced by Automatic defrosting.