Just starting yesterday morning my truck is makeing a funny noise. When I downshift esp. if you let it slow way down in 5th and 4th gear it sounds a little like an exhaust brake going off but not nearly as loud. It seems like it's coming from the clutch area but i have not been able to confirm this. The truck has 90,000 miles on it and I have only had it 3 weeks I thought the clutch seemed pretty good when I got it and i haven't noticed it slipping. Anyone have any experiance or advice?