[M235ForNow]

For way too long I've been bedeviled by a mysterious, highly repeatable, noise. It sounded like a coin sliding back and forth against hard plastic, occurred during hard(ish) acceleration or deceleration and sounded SO much like it was coming from the area of the right passenger door. Emptied the door pockets. Didn't help. Maybe the rear door pockets? Oh, right, there are none. Wait - maybe it's the passenger seat belt buckle sliding against the door frame in a pendular fashion. Nope, not it. Something in the arm rest storage bin? Certainly there was stuff there. Emptied it and ... no change. Under the ash tray cover? Nope.

I got my wife to sit in the back and she thought it was coming from the trunk. I flipped down the seat behind the driver so she could really be sure. Yes, she was pretty sure it was coming from the trunk. So we traded places, me sitting behind passenger seat and her driving. And what I heard was noise coming from ...

Any Sherlocks want to guess what I heard and what was the cause of the noise?