on the drivers side rear, there is a metal round wheel mounted on rubber just sitting there attached to the frame.

what is this for?????

 

any pics?

 

We need more info on your truck.

 

it there to make you ask questions! sounds like its doing its job Lol.
what color is it is it a light green or a fadded blue?

 

I know my truck has something similar to what you are describing it is to get rid of the shake that the truck has...Mine would shake and vibrate at high speeds the dealer put it on my truck and it stopped the shaking maybe its the same thing?