Mine definitely does not do that. Does it still rattle when the grips are off? You might want to give Smith and Wesson Customer Service a call and ask them what the rattle might be.
Yes the first thing I did was remove the grips. Nothing in there. It makes this sound with the hammer in any position and while holding the cylinder still. Sounds like it's coming from behind the side plate where the majority of the mechanics are located. The trigger also feels much rougher then I would expect as compared to my TRR8. The TRR8 has had 1 visit to the factory right after purchase. Maybe this will have to take the trip as well.