[motoretro]

If you replaced the rubber bumpers and greased all the hinge points, the noise is probably coming from the two piece hinges that rattle when the tailgate is closed. With no tension on them in the up position , they tend to swing back and forth in the hinge cavity(area between the gate and bed post). You can rtv thin (1/8") rubber pads in the hinge cavity. This will give the hinges something else to hit on besides the cavity's metal sides. Worked for me. Good luck!