I have the following setup...an Avic 910 nav unit running into an Infinty Kappa 5 channel Amp powering polk speakers. The Infinity Amp is in the trunk with a 4 guage wire connecting directly to the battery and 4 guage ground to the car chassis via a big bolt. The RCA are long, but good quality (I think they were monster cables).

I am getting a high pitch alternator whine (varies in frequency and amplitude with engine RPM). The Volume does not change when I change the volume of the radio...ie if I turn the radio volume to 0 I still hear it as loud as when the radio is on full. With Music pretty loud I cant really hear it but any thing else I can. It does NOT make the noise with the car off and on Accessory (of course the engine is not running).

I tried the trick described in these forums to ground the RCAs to the chassis of the radio. This made no difference. I tried to run a ground strap between the radio and the amp, again no difference.

So I am at a loss here and it is driving me crazy. I dont really know if it is the radio or the amp to be honest. I was wondering if perhaps it is the AMP...is there something else I can do here? Could it be on the 12 volt line to the amp? Is there some filter i can add...would one of those big capacitor help?

Any suggestions greatly appreciated

Try a different ground spot for your amp. Yes they do make ground loop isolators.

To isolate the component that is causing the issue, disconnect your amp and hook up a few speakes directly to the head unit. If you still have the alternator noice then it is the head unit grounding that is the problem. One thing I noticed on mine is that the wires in connectors don't stay in very well, so after you plug the connector to the head unit, push all of the wires in to make sure they're seated properly.

As for the amp, you mentioned that it's grounded with a big bolt. Make sure that the metal where that bolt is, is not painted or rusted. If needed, use some sandpaper to clean it down to bare metal to ensure a proper ground.