Alternator whine

[amagalla]

OK. I need some help here. I've narrowed down the source of the alternator whine to the head unit (HU). The way I did that was I replaced the HU with another (an Alpine unit I have here) and the noise went away. I used all the same electrical connections. So, it look like my HU is sensitive to noise. I tried grounding the RCA plugs. It only added more noise. My question is: How do I eliminate the noise in the HU? I've tried a better ground, noise filters (of questionable quality) on both constant and switched power. Any other advice?

Thanks.

Tony