I'm hoping someone on the forum can help me diagnose this problem... I have a 2000 F350 SD 7.3 / Automatic 4WD short bed with 117K miles on it. The truck is used for towing an enclosed trailer (racecar - about 7800lbs loaded), mostly. Over the past 6 months or so I've noticed a pretty loud hum or rumble sound when the truck is idling. The hum is a little louder when it's in gear but it's there all the time at idle. Everything is stock - no chip or intake/exhaust mods (yet). The truck is rougher at idle lately and there is a slight vibration at idle as well. Everything else seems fine - still pulls like an ox with the trailer... any ideas? Thanks. Jeff M

 

Torque converter maybe. They normally have a metallic rattle, like marbles in a can.