Model: 006 BC4 PNP 3 years old, already installed. Was whining. I thought it was the replacable cartridge/impeller and replaced it. It wasn't. Still whining. Seems to be moving water, but just whines. 1) Is this common? Is it due to having the unit on a timer? 2) I assume it's in the motor housing, and will drain/disassemble to investigate. Can I run it dry momentarily just to investigate? 3) If I need to replace the whole assembly - and I'm assuming that I can reuse the sweated "base" (the rest of the housing just bolts on with a gasket) are there less expensive models that I can use instead, that will still fit the base? Thanks!