Mine makes a little rattly sound, but it is from the 'bumper' case that it has on it. The contacts on the bumper make that sound for me. When I take the phone out, it is silent when I drop it from a half inch or so (other than the clunk sound the phone itself makes).

Dropping the 'bumper' by itself also induces the rattle sound.

Other than that, I have not heard of any iphone4S rattle sounds. Does yours have a 'bumper' case on it?