New Member. 2005 / 2500 HD 4WD/ Ext Cab / Auto Trans. 126K miles. Mostly highway use. Rattling noise underneath, towards front. First time to dealer - they said the right front wheel assembly was bad, so they changed it out - $ 620! Think I got took on that one! Exactly one week later, exact same noise, again. Back to dealer. Said they couldn't hear it - everything checked out okay. After 4 test drives (last one w/me) - they finally said at first they thought it was catalytic converter, then a loose baffle in muffler. Sporadic - though it seems to get louder the longer I drive. Truck runs great - no overheating, no rear end or tranny noise. Clueless at this point.???