I heard a dog walking!
Its not debris at all. It sounds like the impeller is hitting something randomly. Can you verify that it spins freely? Otherwise I would say its a bearing/washer/driveshaft issue. Those can be replaced here:
http://ecotechmarine.com/parts-store/
I would call echotech on Monday, send them the video link and they may pinpoint exactly what it is and what you need to get to fix it.
So I'm even more glad that you figured out that this MP40 is a "her". Find her a "him" MP40 and we're in business!