Have you had a passenger in the back seat ride along to help discern exactly where the sound's coming from? I had to do that to locate a rattling sound that cropped up... turns out I had not quite cinched down the tire jack/lug wrench when I took it out of the car to inspect the spare tire and familiarize myself with where everything was stored. While driving, all I could tell what that the sound was coming from the rear of the vehicle and I was fairly certain is was inside the vehicle, but couldn't even be certain about that.

Let us know if you figure out what it is and/or if it's corrected.

- Shannon (Geeky, Wild Texan)