I recently installed a new headunit in my X that accepts a 1/8" stereo line in on the face. I hook my MP3 player to this connection. When running the player on batteries I have no problems, but when it is plugged into a power point (DC) I get feedback. The MP3 player has a hard drive, and whenever it spins up I hear the clicking of the drive access through my speakers. When I turn the unit off, it gives the speakers a good pop (kind of like the sound when a sub gets flipped on/off).

Since this sound only happens when the player is hooked up to vehicle power, I'm thinking it's a bad ground connection somewhere. I spoke to a local stereo installer and he suggested hooking the player to an RCA input on the back of the deck, which I may try eventually. He said that 1/8" stereo connections are prone to noise and interference.

Any ideas? I'm about to do a few experiments to try to isolate the problem, but wondered if anyone had any input.

Thanks for any help,
Brad