Could also be something caught in the impeller, which would be fairly easy to remove, if you're handy enough to take the motor apart. I'm not....but in having some general maintenance stuff done last summer, the service guy removed a golf-ball sized ball of nylon pieces (rope disintegrated), brush bristles, grass, and other debris from my impeller. He told me that it would have soon seized and the impeller not able to turn at all.

Janet