I just started listening to the radio again after a long spate of not, and I noticed that there's alternator noise when I'm listening to the tuner, but not when I'm listening to mp3s. (I don't have any Aux hooked up right now.)

Any ideas as to why? I need to open my dash anyway; the tuner module has come loose from its moorings and is rattling around in the dash somewhat anyway. Maybe that has something to do with it?