i have a 2004 f-150, i can push on the tailgate when it is up and hear a squeak. also when i drive on gravel parking lots i hear this squeaking coming from the back of the truck. does anyone have any ideas on how to fix this, i have looked everywhere to see what is rubbing.

 

Could try putting a thin layer of grease on the rubber bumpers mounted to the box where the tailgatemeets the box. Hope it helps.