Hello folks. Bit of an issue. I have an older, used Pro Mag that was sold to me with my (new to me) Beretta CX-4 Storm, as he lost the original magazine. Anyhow, I can load it up to about five rounds with no rattles, but beyond that, it sounds like a macarena shaker. I've unloaded it at least five times, and reloaded it, making sure the bullets were "alternating" left and right. Ammunition is UMC 9mm 124gr., if that makes a difference. I also have four brand new K-mags, and other than being crazy-tough to load, they don't rattle one bit. The Pro Mag in question is not as tight, but still plenty stiff.