Hi everyone! I'm worried about my goldfish. Please help! My pond has a waterfall feature. The pump that gets water to the top of the waterfall has quit working. I've checked: no blockages (able to use a hose to force water through); filter is cleaned; impeller is spinning freely; I don't see any leaking seals. It does seem like the impeller is rattling around now, but is held in place by magnetism, nothing to tighten or change. There is power, no blockages, no airlocks... And no suction with the tiniest if rattling noises that wasn't there before. Why won't it work?