Just got my '07 back yesterday from the dealer for exactly the same thing. It was aggravating because it would come and go and seemed to act up more in warm weather. Anyway they took the entire left rear panel window out, tightened some loose mounts and ad-hoc engineered some extra insulation around the window. So far so good. Now I can just focus on the occasional trunk thump but I can live with that compared to the chirping. Drove me nuts.