What is this and what is it's purpose?

[GTS RAPTOR]

The other day when I was installing the wiring for my Rigid dually LED aux rear lights, I noticed this thing and wondered what it was and what it's purpose was.
It's located on top of the driver side fame rail above the spare tire.
It's 12" L x 4" W and looks like it's connected to the frame by two bolts that have rubber bushings?, I can rock it back and forth easily with one finger.
Could this be a damping system or maybe a counter weight?
Anybody know what it is and what it's purpose is?
Just curious.

 

[bstoner59]

I believe that is the 10lb weight that gets lose and creates all the clunking guys have been complaining about.

 

[MarkT]

I believe that is the 10lb weight that gets lose and creates all the clunking guys have been complaining about.

That's the weight... According to the Ford guys at the last Roundup, it's one of many damping devices to improve the "NVH" (noise, vibration, harshness) of the Raptor.