Whenever I use the brakes after moving forward following driving in reverse I hear a series of metallic clicks from the rear of the truck. Recently rebuilt the drum brakes, no broken springs, fully functional so I don't believe that is the source of the sound. Does anyone have any ideas on what the problem might be? I haven't noticed any loss of functionality or any rear end noises otherwise.

Probably not specifically relevant but its a 98 F-150, 4.2L, 2wd.