i just bought a mp3 this week. it has 13,500 miles. still under factory warranty. it was making a noise on the passenger side rear when i go over a bump. it actually sounds like the spare is bouncing around but it is not. checked the exaust, it is fine. it sounded like the strut was bad. i took it in and they said they could not find anything wrong and they tightened the rear sway bar and the noise stopped. but, now 3 days later it has started back up again. what could this be? any comments would help. this is my first post.