Have a 96 dodge with a 5.9 gas with 141k miles it makes loud raddling noise when i shut it off and there is an occasional knock when when going down the road.

 

First thing that came to my mind is the torque converter bolts being loose. Crawl inder the truck and remove tc shield and check the bolts.

 

There was a recall on the catalytic converts, Might want to hit with something and see if you hear anything.

 

could be all sorts of things ...I would crawl around underneath and check everything for looseness - all exhaust, hangers, etc... cross members and mounts, starter,engine mounts, etc... if nothing becomes obvious at that point, have someone else start it while you're underneath and see if you can see something or at least hear more clearly where your "clanking" is coming from)...