Anybody familiar with car audio install?

[BStecke]

If so, I've got a problem with the system in my fiance's car. Whenever the dome light is set to "auto," there is a VERY loud buzzing coming from the front speakers. She's got components up front, fed by a Polk audio two channel. If you disconnect the RCA's and fade the audio to the rear speakers, fed off of the radio, there's no problem. We've swapped amps and RCA's, so the problem is somewhere up front. When I take the radio out (Pioneer DEH-P6800MP) and plug it back in, the buzzing isn't there until I open the door, activating the dome light, and then close it. As the dome light fades off, the buzzing fades out with the fading dome light. If I turn the dome light to "off" or "on" the buzzing stops, but if I switch it back to "auto" it buzzes. I've checked the connections and can't find any problems anywhere. Any help would be greatly appreciated.