tailgate
There's a bump stop on either end of the tailgate as I remember, might be rubbing on that. Might try wedging some cardboard in there to tighten it up and see if it still chirps on you, might be coming from somewhere else.
lol thats about the only place it can be making that noise at there is one on the other side to if you know how to take it off you can check the other side to it dont take 30 secs to take it off


