I have a 2002 myself and have been doing a lot of work to it recently. any chance the sound disapears when the guage/radio trim/bezel is off?
I found it most interesting that GM put a micro bead of rtv like substance around the inside edges of the bezel to eliminate squeaking and vibrations. I wonder if that's deteriorated or fallen off on your car and is the cause of a squeak that you hear.