rubbing on something... inner fenderwall... or something busticated in the rear suspension, i'd narrow it down but i've never really looked at the rear suspension in this beast. the only car i've ever had in which i played with the rear suspension had a single fiberglass leaf-spring, or mono-leaf spring. (yes old corvette suspension, and yes i haven't installed my rear lowering springs yet)
this is more common on the newer dodge trucks but they come from the factory with... um for lack of better words... a bent axle. Basically it causes alot of inner tire wear. It is a warranty issue from the dealerships if anyone notices, or tries to get an allignment and still is getting the inner tire wear.
Other then that... um. low-inflated tires with alot of fishtailing and cornering??