Electrical Issue: Radio (AUX) Interference

Prior owner had an aftermarket head unit installed (Blaupunkt MP3000).

Unit features L/R composite audio-in at the rear of the radio. There's a 3-ft cable run from the input jacks out to a standard stereo 1/8-in male connector so I can plug the iPod or Sirius in.

The problem appears independent of whether there is a device on the other end or not, merely plugging the left and right composite plugs into the back creates interference and it doesn't get worse between the iPod and Sirius, it's consistent between the two.

The interference level (or intensity maybe?) changes depending on many factors. I'll go from low "level" to "aux useless" level:

1. Vehicle engine off, lights off, radio on in AUX mode.
2. Vehicle engine on, lights off, 4x2, radio on in AUX.
3. engine on, lights on, 4x2, radio on in aux.
4. engine on, lights off, 4x4, radio on in aux.
5. engine on, lights on, 4x4, radio on in aux.

When accelerating, it gets worse and seems to become more intense the higher the RPMs go, so driving in traffic makes all kinds of noise!

I tried grounding the radio, attaching wire to the radio, the other end to the frame. No such luck.

Luckily AM/FM/CD work fine, but I'd really like to get this AUX to work correctly!

Any ideas of the cause?

I did just buy a heavier gauge + shielded audio cable from Radio Shlock, but haven't tried it. Will report back once I do.

Any help would be greatly appreciated.

-Douglas

(2000 Passport LX 4X4 Auto)

Sounds like alternator noise. I don't remember but some alternators have a little capacitor mounted on the back. That's a noise suppressor. If it's gone bad that would be your problem.