I've developed this noise on my 2wd prerunner. It sounds like it's coming from the axle and only occurs when I apply the brakes over broken pavement or dirt. It appears to be a result of the rear tires intermittently getting traction. It's a metal clanking/shifting sound that sounds very similar too say your u-bolts were loose or maybe you left your hitch in over a bump. Thing is i've checked all the bolts, hitch is out, and everything seems tight, even the spare tire. I could hit some nasty little washboard road and never hear the sound until I brake. It's seperate from the front brake pad clank. Whatcha think? Axle wrap? Something loose in the rear drums?
Only relevant mods are add a leaf, rims, tires.