What is this part above my frame rail for? It is loose and wobbles side to side. I'm pretty sure it is one of the vibration noises I hear when I hit a bump.

 

It's one of the assembly line workers lunch pail. He set it on the frame rail after lunch and they dropped the bed on it.
Actually it looks like one of the many "fixes" that manufacturers put on vehicles to correct the problems when the design engineers and development test people drop the ball. (all of them do it more often than you think!) Though I've never seen that particular one, it is probably to deal with a harmonic sound or vibration.

 

No idea. My truck definitely does not have that.

 

I got one too, my dad says its for vibration dampening. not sure how, or why, he thinks that.

 

I've read on here and other forums it's some kind of vibration dampener. It does come loose and cause a clunk when going over bumps. From what I've read most guys just remove it.

Mine doesn't have it so I'm not really sure.

 

My '07 FX4 Flareside has that weight over top left rear frame rail, it's rubber mounted (in that the mounting bolts go through rubber bushed holes).

My bed does NOT shake at any speed I've ever seen ......
...... but I recall some guys having bed shake problems and not having that weight ..... so I will keep mine in place.

 

it is a vibration dampener, I have replaced them under warranty before and have even removed them outside of warranty. I never noticed a difference on or off except no more rattle

 

I just looked mine over real good. It doesn't have one.

 

So it is not supposed to be loose?

 

Mine is in the exact same place. I will leave it installed also. Thanks for the info.