There is a problem like that with the xd-45 mags. The first round in the mag (at the bottom) Doesn't seat well and rattles. But only when not inserted into the gun. When pressure is applied to the top round the rattle goes away. You can hold your hand out and smack it against it. This may get the rounds to seat better in the mag. If that doesn't work, consider putting the mag in and slamming it into the gun, this might put a bit more pressure on the bullets in the mag and stop this. DO all you mags do the same thing?