so i have an on and off rubbing sound coming from my rear under and am having trouble determining the source. at first i thoght maybe the carrier bearing was drying up but i'm still not sold on that. i verified that all the u-joints were still good yesterday so now maybe i'm tinking i have a drum brake going bad maybe? the rub almost sounds like an air leak but my exhaust has no leaks, and the higher the rpms the faster the sound. any thoughts? truck is at 68k. thanks guys.