pnichols wrote:
I've had the exact rattle for years in my 2005 E450 motorhome chassis. It started after we had owned it for a couple of years maybe with 15K to 20k miles on it - just like the OP.
EVERYTHING has been checked by me and others down there underneath ... all shields, mounts, brackets, torque converter cover, etc..
I'm convinced that it's probably some of the guts of the catalytic converter loose/broken and rattling at certain speeds and/or heat conditions. If catalytic converters didn't cost so much, I'd just replace it to get rid of the occasional racket. However, it seems like in the last year or so that the rattling has maybe lessened a bit and is not so irritating. (By the way, alternatively, is there some kind of a resonater in the exhaust line that could have loose parts rattling around inside of it?)
I'm very interested in what the OP discovers it is if they pursue it all the way, including installation of a new cat converter.
Also there are baffles inside the muffler that get rusted and can come loose. I would tap on the muffler, cat and resonator if you have one and see if it rattles.
