Sounds like a Detroit Locker, kind of a ratcheting noise when turning (while light throttle or coasting). "click click click". If you give a little gas while turning it will lock and on drive pavement will chirp the tires a little as they are now spinning the same speed. Or you can jack up the rear, put the truck in neutral and try the locker test, look on youtube for this.
Many times a Detroit Locker will be put in a nodular third member. If there's a big N on the third member housing, it's a nodular. These are beefier units.