Noise from the Head Unit

I seem to be getting noise from my head unit. It is evident in what seems to only be my rear speakers, but is evident weather amped from my amplifier using RCA's, or from the head units speaker output. I get alternator whine, and the heater fan also interfeers. Also whenever i turn something electrical on i can hear a small click or pop. I've tried earthing the head unit directly to the battery but still have the problem. Any ideas? is the head unit at fault? or something to do with the cars electonics or whiring. Its an old ford orion (im in the uk) if that makes a difference. Thanks for looking.

The speakers are wired using the standard ford wiring when using the head unit as their power, but usually are connected straight to an amplifier in the boot (or trunk as you call in in america). The noise may actually come from the front speakers and tweeters as well, but if it is, it is very very quiet. I will try connecting the rear output to the front speakers tomorrow. I'd also like to point out that adding a capacitor across the constant +12v and ground, the noise decreases in volume very slightly, but its still loud. But the capacitor got rid of the ignition clicking noise. I don't think the noise is induced though, as when i run the system from a seperate personal cd player (aa battery powered), there is no noise. Do you think the head unit is defective?

You might also want to wire the constant and switched together and run a wire for them and one for the ground and connect them to the battery, and see it the noise goes away. But connect the rears to the front because that will tell us a lot. Also listen and also tell me if you hear the noise in the fronts.

Right, i've tried connecting the head unit power using seperate wires outside the car directly to the battery with no sucess. I will try connecting the rears to the front if i get time tomorrow, but ive listened to the fronts and i can not hear a noise. Today i tried a capacitor directly on the alternator but still noise. Cheers

I've solved my problem. I borrowed a friends head unit to try in my car and there was no noise at all. So i came to the conclusion that it was a fault in my head unit. So i took it back and got it replaced for an identical head unit. I plugged it in and it was fine, no noise. I think the ground path in the old head unit must have got damaged somehow. Anyway, thanks for your help bberman1, i appreciate it! Cheers!