I have a metal vibration coming from the passenger seat intermittently. It sounds like a 'buzzing' or a 'metal on metal' vibration and usually occurs between 40-50 mph with light throttle applied. I removed the passenger seat and drove the car and the sound went away. I don't think it's the seat belt because I've tried using the clip and also having the belt fastened. The sound also goes away when there is a passenger. The sound is loud enough to annoy the heck out of me!!! Anyone have this problem or a solution?