^^^ That's one of the things I suspected, but since I've had it apart and back together quite a few times (for cleaning, media change, etc) and I'm sure I haven't misaligned it every time. Is there something else that might be able to become lose, or possibly the motor unit itself wearing out?
wgf97079 - how old is your magnum? (and yes, you can get new impellers/motors for them, check bigals).