So basicly I have a double bell scar it uses the army armament gearbox according to the book my one is making a loud screaching vibraiting nice from gearbox or motor I have no idea how to begin to work on this as only used a pistol before when tecing . Dose anyone know a gearbox that will fit straight in to the gun as is I have taken motor out it defently works . It was working fine was shooting in back garden and put one mag thro it then it's just what I can assume as jamed badly please help