Is this possible the infamous rattling from the tranny problem that many of us suffer from?
I think that XtremeRS diagnosed it as a the throw-out bearing vibrating a bit under idle when the clutch is not depressed. I had this issue on my car as well, and it normally sounded MUCH WORSE in the winter, and bearable in the summer upon warmup of the car.
Some people say replace the TO bearing, but when I installed my built engine and new clutch w/ to bearing, I STILL had the same problem.