Air compressor breaker tripped, seems like motor is bad. It's a 7hp 60gal unit, motor is AO Smith 3450 RPM, 220v. I can rotate belt freely and hear bypass on compressor opening, so there's no resistance to motor starting. When I close the contactor on the pressure switch I hear a very loud humm and vibration which will trip breaker if I leave it on more than a short instant. Motor turns freely by hand. We have local places that rebuild motors, think that's the best way to go, or just buy a new motor? No idea what these cost.