gjin,
I know this is a old post but I wanted to put my two cents in on the buzz... I had the same problem and it was not a ground loop or a wiring problem but it was the head unit... I took it back to where I bought it and they had it sent back and when it came back it was all fixed... The service guy noted that it was a problem that is seems to pop up from time to time... I even went as far as having my front speakers in my Tahoe replaced because I thought that is what is was at first... So just my little input...
