Buck Rogers , May 29, 2006; 12:18 a.m.
I have had one for about a year and a half. It didn't do it when I bought it nor. After a LOT of abuse (the barrel is now cracked) it still operates flawlessly with no rattles.
If you exchange it, does your replacement warranty period restart? If it does and you get the same problem, at least your better off with a longer warranty period.
Regardless, it sounds like a defect and it may cause additional problems that might end up at your cost to repair.