i hear a loud grinding or clicking noise from the rear wheel when i accelerate my razor e300.

Diagnosis

The motor's drive pinion gear is grinding against the rear wheel's gear. This is almost always caused by a loose motor mount.

How to Fix It

Tighten the two motor-mounting bolts.

1. Turn the scooter upside down.
2. Locate the silver motor casing attached to the frame near the rear wheel.
3. Use a 10mm wrench to firmly tighten the two bolts securing it. Do not overtighten.
4. Spin the rear wheel by hand. The grinding should be gone.

If That Didn't Work

The gear teeth themselves may be worn or damaged from prolonged grinding. You'll need to replace the rear wheel assembly (the driven gear is part of the wheel) and possibly the motor pinion gear.

Heads Up

Riding with this noise will quickly destroy the gears. Stop using it until the mount is tightened or gears are replaced.