Do Any Of Your Magazines Rattle?
It all depends upon how the magazine spring sets when the magazine is fully loaded. Take two magazines apart, and mark each spring: one as, ‘good’ and the other as, ‘bad’. Then, carefully examine the spring on the magazine that rattles. Look, first, for any twist of the magazine spring’s body around its vertical axis. If you see any twisted coils then straighten them out. (You want to match the twisted, ‘bad spring’ so that it looks just like the straight up and down profile of the, ‘good spring’.)
Next, with both springs still out of their magazine bodies, take a look at the pitch and angle of the magazine follower. You want the, 'bad spring' to have the same, ‘pitch’ and, ‘yaw’ as the follower on the, ‘good spring’.
Sometimes a follower might be nicked or need to be replaced. An interior magazine body might, also, need to be smoothed out by having any excess, ‘flashing’ or rough metal edges polished flat. (Use a polishing agent like fine emery cloth attached to a tongue-depressor. I, often, wet my emery cloth with oil in order to put a fine burnish on a metal surface.)
The top, and bottom coils of a magazine spring require special attention; so be sure to look at them carefully. Make certain the magazine follower and the lower insert are in good condition.
If you can’t identify anything that’s either different, or out of place then you've got two options. (1) Install a new spring, or (2) leave the, ‘bad spring’ you've already got fully loaded and inside the magazine body for an entire week, or more. See if that helps.
[COLOR=RED]ADVISORY[/COLOR]: I am NOT a Certified Glock Armorer! (I'm only that armorer which Gaston Glock has forced me to become.) ;)