I think you're in the same boat as me. My view which can be incorrect, is that the squeak your hearing "from your timing belt", is the bearing spun around your crank slowly breaking loose your rod if not already. Eventually it will turn into a chatter as the rod can move more freely around the crank while in motion.
If you stick your head under your car your gonna hear it a lot better and in more detail then the squeak you can just muster from the top.
Sorry if you already mentioned but what exactly were you doing before you noticed the noise?
I know this is not a supra but the stage this corvette is in is exactly the stage both of cars are in relation to progression of the issue. The Corvette has already started to chatter.
http://www.youtube.com/watch?v=gRSrUQudaP0