I've got a clunk in my rear axle/suspension that has creeped up over the last few hundred miles (Im at 50,000). Its sounds just like a single clunk, and Ive narrowed it down to being outside the VX, and from the rear (nothing inside the truck). It makes it going over small impacts, bumps etc at low speed (0 - 35 mph). I can also duplicate it by going in reverse at idle speed, then locking the brakes. As the VX settles I hear the clunk. Doesnt do it forward with this lock test, but only does it when driving as mentioned above. I did try the reverse brake lock test with a slight drag on the parking brake and it seem to get ride of the clunk. Could my rear parking brake shoes be loose or need adjusting, and are clunking over bumps, etc? Does anyone have a proceedure to do so?

Thanks