Humming noise when heat/AC is on?

[KyleNatolix5]

I noticed I get a very annoying humming noise when I turn on the heat. It makes a two tone sound in a steady pattern. When I turn off the heat the sound stops immediately. Any ideas?

[740ilDuke]

People rarely (never) service the compressors until they are already making noise - which is what you are hearing. The oil in the compressor gets tacky then it makes a knocking sound. My E38 (same compressor) has a relatively loud one. You can service it and have new oil added, which may help. Certainly can't hurt. Otherwise - replacement. Im going to let mine knock all it wants until it dies.

[Qsilver7]

Originally Posted by KyleNatolix5

I noticed I get a very annoying humming noise when I turn on the heat. ... When I turn off the heat the sound stops immediately. Any ideas?

From where is the humming noise coming? The engine bay, behind the dash, below the center console, etc?

BTW, do you have the rear climate control option on the vent at the back of the center console? If so, and the sound is coming from that area...try turning that blower off to see if its the culprit.