An underbody splash shield (one of three, I believe), covering the transmission (the middle of the three) detached at highway speed and fell off the vehicle. This caused the leading edge of another shield to detach, which then, due to air flow, began dragging the highway. It was quite a noise; initially I thought it was a tire blow out. I quickly decelerated to try to move to an exit (it was urban highway with no shoulders), at lower speeds, the panel stopped dragging. There was no road debris involved in the event. The first panel simply detached (and was not recovered / recoverable due to the location) leading to the second. The initial mechanic replaced two bolts to secure the second panel. He said this is not uncommon on Mercedes Benz vehicles and seemingly knew exactly what was needed (I was expecting duct tape on a weekend morning). Later, after some discussion, the dealer (the car was under warranty; only 13,000 miles) replaced the missing panel as a "courtesy" but not under warranty (because they said I did not have the missing part).
NHTSA ODI 11611928