DIAGNOSIS Debris like hair or sand is caught in the rotating scrubber brush mechanism under the washing plate.
FIX Power off the dock. Lift the washing plate out of its slot. Visibly inspect the rotating nylon scrubber brush. Use tweezers to pull out any wound hair or threads from the brush ends and axle. Manually rotate the brush to check for grit.
IF THAT DIDN'T WORK The scrubber brush motor gearbox has failed. The noise is stripped plastic gears. This requires replacement of the wash module assembly inside the dock.
HEADS UP Do not run the wash cycle with this noise. It can shear the gears completely, leaving debris in the water system and requiring a full module replacement.