[Flieger]

There's a chapter in Rob Siegels book about getting cars free from rattles, squeaks, and clunks. He says seats (at least on older cars) often make noise from the rails and he will remove a seat and drive the car to determine if that is the cause and then move on to the next noise which could be a trim piece, etc. But on a new car I don't know what it would be other than a heat shield or exhaust hangar. And you probably don't want to start taking the back seat out.