If I strike the plastic running board with my fist toward the rear I can hear something rattling around inside that sounds like a small rock or two. I hear this on both sides.
Has anyone seen this? How could one remove this gravel?
The first post in this thread discusses removing the running boards to install some lights. Maybe you need to disassemble it and turn it on its end to remove the pebbles?
If you are lucky then they might be located in the end caps?