Yep, sounds to me like a case of a stuck brush. If you haven't cleaned your motor lately i recommend you do so. To clean the brushes you just unlatch the spring and then unhook it from the post.. The brush should just slide out after the spring is out of the way. If your motor needs to be cleaned, it probably also needs to have the comm cut and the brushes cleaned up with a 'comm stick' or some other way of cleaning them off.