I am another victim of that annoying rattle when the a/c is on. I took it to the dealership and they said the compressor was bad and needed replacement. It was replaced and right when I picked it up I could still here that annoying rattle. It was covered under warranty so i lucked out with a free compressor, but still have that noise. Any ideas on what it could be since Chevy can't even get rid of it? I just love it when I bring my truck in for a certain problem, have it sit all day at the dealership, and then when I pick it up nothing has changed...good ol' Chevy!