My 2hp pentair whiperflo pump hums initially when turned on. I turn the pump on and off a few times letting it hum for a few seconds each time. The pump will then eventually start. After the pump is up and running, it sounds normal and everything appears to be functioning. The capacitor has been changed with same results. I can't move the impeller by hand even though nothing is stuck in the impeller. I can move the impeller using a wrench on the rear shaft.