Search interior rattle on this website. People have posted several good ideas to try. I did find that if I sit in the middle of the rear seat and go over a rough road surface, the rattle is not as bad or gone. I’ve looked under the seat for areas that could cause a rattle. I put rubber spacers in those areas. When NOT riding in the back seat the rattle is still there when going over rough surfaces. I’ve given up trying to find the problem. Very frustrating. While this is a very occasional issue, I’d like to get it corrected. As much as I don’t want to, I will take it to a dealer . Hopefully they have had this problem before or can get it corrected. I will post if the they find something. Otherwise, our Corsair is a great vehicle.