I have a 99 D1 in which I have installed a rebuilt radio from John at GB 4x4 Radios, a rebuilt woofer and some nice new mid ranges. This radio works great on any of the broadcast freqs, and using the aux plug on something that is running on it's own battery power, but when I plug in the aux to whatever device is running from the car power(e.g., cigar lighter bluetooth, iPod thats charging using cigar lighter, etc) I get a lot of noise coming through to the speakers. I have wired a totally separate aux power plug setup direct from the battery to the aux power plugs, complete with a 25A capable noise filter inline. Does anyone have any input on where this noise in the car system emanates? Could it be the alternator itself? I will add that the noise changes in pitch with RPM.

 

Make sure to check your ground connections, I had the same issue and it was related to dirty ground connections