The front wheel bearings have been tested and replaced if necessary.
Next Step: Test the Rear Wheel and Motor Bearings
Lift or block the scooter's rear
wheel off of the ground, turn the scooter on and engage the throttle
around 1/8 of a turn. With the rear wheel slowly spinning listen for the
grinding noise in the rear wheel area. If the grinding noise is
coming from the rear wheel area then the problem may be the motor
bearings or the rear wheel bearings. To determine exactly which
component's bearings are making the noise turn the scooter off and
remove the chain from the scooter. With the chain removed spin the
rear wheel by hand and listen for the grinding noise. Then turn the scooter on again and engage the throttle a
little to spin the motor and listen for the grinding noise in the motor.
Replace the rear wheel bearings or motor if necessary.