I ordered 4 mags from GMW. Three work perfectly. The fourth is difficult to load the twelfth round and when doing so, there is a distinct rattle from within the mag. Take a round out, so there are eleven rounds, the rattle disappears. I have disassembled the mag and all looks to be normal. All other functions with this mag are fine.
This was true of a lot of the HiPower mags I have had over the years. Rattle when full, stopped rattling when you take one out. I wasnt able to find the cause, and it was pretty hit-and-miss for a long time