[Larken]

The buzzing sound is the short ciruit protection circuit tripping out. You may have a bad motor, possible with a shorted winding to the frame or some other short. Check the motor that there are no metal chips(turnings) inside that cut into the insulation.

Its possible that you've blown a mosfet in the Z axis drive. The Mosfets are a IRFP4232 . Its best to change all 4 mosfets and the IR2104 drivers at the same time.

Or, I can send you a replacement board

Larry K