Assuming you have ruled out the very commom rear hatch rattle on Coupes, I would start at the exhaust first. I found an exhaust rattle on mine that took me two months to find thinking it was hatch related. It only happened when hot as the the system expands enough that the muffler would move back enough that the muffler mounting flange rubbed slightly on the mounting bracket fixed to the car. The system actually moved 3/8" when it got hot. Good luck...rattles drive me @&#* nuts!!