iPod in car, noise problem

Car: 1989 Mazda 626

Headunit: JVC KD-G615

iPod: 1st Gen Mini

 

Just finished up installing my iPod Mini (1st gen) into my car for the second time. Previously it used the aux-input on the front of my headunit, but now I've got an adapter so I can plug it into the cd stacker plug and make everything neat.  The iPod will also charge when it's plugged in.

My problem now is noise. Previously there was no noise, now theres white noise, you can hear the hard drive when its running (incredibly annoying), you can hear movements from the scroll wheel, you can hear the backlight turn on and off. Everything comes through the speakers.

I've got no idea whats wrong.  I've re-made the cable, checked and double checked everything with a multimeter, given everything a good earth, tried two different RCA noise isolators...nothing I can think of will fix it. 

 

It gets even more strange, with the iPod in the car and the negative and postive disconnected the sound quality is awful, no bass...like its out of phase, but if i connect the negative or the positive the sound becomes good.

 

I really am stumped with this one, any help would be really appreciated.