Brake adjustment is needed to keep the trailer from pushing on the truck when you stop. The hitch pin pushes forward when you stop due to the brakes on the trailer not stopping the trailer with or before the truck stops. Instead of staying seated against back of the jaw or bar the pin moves to the front of the hitch pocket making the clunk when you stop. Then when you start it moves back to the jaws or bar and makes another clunk as you pull forward.
Reducing the slop in the hitch pocket will help but a properly adjusted brake controller saves the truck brakes and is how the system is suppose to work.
