I have a Carrier 2 1/2 ton heat pump air conditioner. When the heat is on and it goes into the defrost cycle there is a very load humming and/or vibrating sound that last up to 15 seconds. When it comes out of defrost I hear the same sound for about 4 or 5 seconds. Is this normal? I have never heard any of my neighbors AC make this noise. It is so load that it sometimes wakes me up at night.
Thanks for any help.