I just fitted a new head unit (empty slot before for some time) and there's interference from the electrical systems that can be heard whether I'm listening to the radio or MP3's (with engine running, no interference just with ignition on). There's a type of constant background whine regardless or revs, and another whine/whistle than increases frequnecy with revs.

I've used the old ISO connectors that I added in to join with the OE Fiat connectors, and all the earths and power supply leads seem to be OK. Is it a symptom of a poor earth somewhere else?

I did get the interference last time I used the old head unit and ripped apart loads of connections to try and stop it, maybe I ripped apart too much, but having put the new head unit in, everything works OK?

Currently the head unit outputs via a single pair of RCA plugs and then splits to amplified fronts and separately amplified sub, rears are still original and go via the standard speaker connections, mayber I should check the speakers/amps one by one. Eventually I will use the head unit to control and amplify all the speakers (although I do like my sub "volume knob" under the dash to quickly change the sub level)

Any ideas what the problem might be?

Ground earth fault I believe. Can be a mare to trace. I had this problem when i added my phones to my system and the phone was charging.

I've had this on my Alfa 147 with a separate MP3 player and ended up with a galvanic isolation module on the RCA plugs for that. I presume you can also put a galvanic isolation circuit (generally a transformer or capacitor) on the power lead(s) to the audio equipment / head unit.

The revs rising whine is probably the alternator you hear. You can fix that with a capacitor close to the alternator. The other stuff might be ground loop.

Haven't read the pages but a quick search through Google:
http://www.sacskyranch.com/altnoise.htm

The problem comes from the separate amp that drives the front speakers, the rear speakers powered direct from the head unit are OK, asis the subwoofwer powered by its own separate amp. With ignition on but even with engine off, the front speaker amp picks up and/or amplifies the high pitched whine but it'a nothing to do with alternator. Earth is to chassis nearby, power is direct from battery (shared with other amp) wirh power connectivity from head unit. Maybe the amp has packed up, I could go back to using direct connections from head unit I guess.

Try changing the route of the rca leads, they may be picking up some interference from a power source such as the power leads to your amp. Or check the earth for the amp that is running the front speakers.

Thanks,I will check that too

duplicate again, damn phone