Many magazines allow the ammunition to rattle. Well, actually, there are two kinds of ammo rattle; like in a drum mag, and in a box mag because of follower tilt. You can smack the mag on the floor plate after it is fully loaded which will sometimes settle the follower. In drum mags, those who carry them and wish to remain silent have been known to cut out and install a disc of linoleum or similar material to silence them.