I have the same problem. I know my pilot bearing is toast. It started rattling really bad upon disengagement(release) of clutch, but made no noise when fully depressed, eliminating the throw out bearing (the way I understand it anyways.). Mine is in the shop now for a complete clutch replacement along with transmission input shaft bearing. I just bought the truck from a local dealer. The muffler had been removed, so I didn't hear the noise on the test drive. When I installed a muffler, it was very apparent, and got worse quickly. $725 for this work. Dealer told me "Too bad, nothing we can do.". I bought this as a project I could use as a commuter while fixing up, but this job was a little over my head. Can't even see those top 2 bellhousing bolts!