ok I can hear it just barely, you might have to get a set of "chassis ears" to chase it down, could be anything a loose panel, a loose component, brake shield, sometimes things will only resonate at a certain frequency and sometimes sounds on these trucks may appear to be coming from one place but are actually coming from somewhere else so you basically have to check everywhere.if you listen closely at around .23 sec in the video it can be heard it sounds like metal on metal flutter/rattle its definitely not the exhaust banging around