DIAGNOSIS: A foreign object is lodged in the wheel module, or the wheel's internal gearbox has failed. Hair and string are the usual culprits.
FIX: Power off the robot. Turn it upside down. Manually rotate the noisy wheel and inspect the gap between the wheel and the housing. Use tweezers to pull out any wound hair or debris. Check the wheel treads for stuck debris.
IF THAT DIDN'T WORK: The wheel module may need replacement. Remove the wheel by pressing the tab and pulling it straight out. Inspect the gears inside the robot's socket for damage. If gears are stripped, the entire drive module (part # RBL100) must be replaced.
HEADS UP: Running the robot with a grinding wheel will drain the battery rapidly and can permanently damage the drive motor. Do not ignore this noise.