Could you define thumping? Does it start slowly and increase in frequency as the speed picks up? Does pressing down on any corner of the cabinet help lessen the noise? Are you sure the front panel is tightly screwed on at the bottom front corners? Have you recently moved the washer? Does the sound stop as soon as the motor is de-energized or does the thumping coast to a stop? We need more detail. As the doctor said, "Constipation and cancer sound the same over the phone."