GM starters don't use a bendix spring? They use a solenoid to move the starter gear over so it meshes with the flywheel gear. On the other end of the solenoid is a copper ring that is pressed up against 2 contacts to connect the starter to the positive battery terminal. I don't see how the starter could come on if the gear hadn't engaged unless maybe something is wrong in the solenoid and is causing the starter to come on prematurely.