on star interference

I recently installed a sub amp in my 2007 Suburban using a PAC that plugs into the back of my factory radio/navigation screen. I recently heard a "buzzing" noise and tracked it down to the microphone mounted on the roof of the truck. Soon after startup, an electronic noise emits from the microphone. The noise does not follow engine RPMs but is a constant "buzz" that is getting annoying being right in my ear. Im NO expert...so I was hoping someone could shed some light on my problem.

The microphone as you describe it, isn't a microphone. It is actually a small fan that has to do with the climate control/air cabin pressure system. If the fan is making noise, take it to a GM dealer to have it repaired. They may have to replace it or adjust its mounting.sparky