I hear a clunking noise coming from the rear passenger wheel.

It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. It could be a broken sway bar link, bad exhaust hanger or many other things but safer to let some one inspect things. Visually look under the truck yourself and see if anything looks abnormal. Get a friend to press up and down on the rear bumper see if you can duplicate the noise.