Pumps rattle, but Mossbergs rattle the most. I used many 590's in the Army, great shotgun. But it's heavy and rattles more than a 870 for sure.
No big deal really, didn't rattle enough on patrol to matter. A 590 will last untill the end of the earth, but the just don't feel as tight as an 870.
U.S. Army 88-97 68W2W1
Operation Just Cause
Operation Desert Shield/Storm
Operation Restore Hope/ Gothic Serpent