So I'm back from my various travels, and I finally brought the car into the dealer last week. Sure enough, I got the radio to make those funny scratching and popping sounds for the tech. He said he thought it was the amplifier (well, duh!!) so ordered one for me. Took a day (that rental they gave me was a POS Chevy Malibu - I was very clearly reminded why I don't buy American iron any more). Now I have a new amp and it's lasted the weekend without any strange noises. Here's hoping it stays that way?

AND - I told them about the rear lid clunk/thunk/rattle. I got the standard speech about how the body flexes and I should expect some clunks and thumps. BUT they replaced the bumpers all around and it does seem tigher. I still have a rattle (somewhat harder to reproduce now) but it seems closer to me, so it may be coming from the passenger side seat belt. We'll see........