Ok so I bought a new S&W sigma .40 on tue. to add to the collection. Anyways, I since loaded the mags ready to take out and test and play with it this weekend and noticed after putting 6 rounds in the mag there is a rattle or a "clank" in the mag. You cant hear it till you put in the 6th round and it doesnt go away with a full mag. Honestly it sounds like a loose round moving around in there. Even worse its just as loud in the gun. So my question is, to all those sigma owners... is this common or what?? If so thats terrible. These are the 2 mags that came with the gun when I bought it if that makes a differance. Thanks in advance for any help...