I just did so myself, you need to access the insides by removing the side pannel, near the deck assembly next to the belts is a circular motor with a small black rubber on it, you need to use a small plastic screwdriver (using a metal one will make the potentiatometer speed up temporarly, it just makes adjusting it harder becasue you need to take the screwdriver out) and turn left for slower and right for faster until it sounds normal.