I'm a newby to AP, but have some experance with constructon "trash" pumps. If this is a submersable, I would look a the entire suction side, pipes, filters, for any kind of restriction. Or even the inlet too close to the bottom. If it is not a sub. again suction side. Put some FT water in a spray bottle and spray liberaly around all fittings and watch for the pump to quit cavatating. The water will seal the air leak, for a few seconds and you will know which fitting needs to be resealed. Best to you!