engine noise

I have a1999 dakota and have a noise in the rear of engine around the bell houseing the truck has 80000 miles and uses no oil between changes has good oil pressure and runs pretty good for a 3.9 . have changed distributers twice, and replaced a clogged catalic converter , and the noise started just after replaceing converter. any help would be greatly
appreciated

Double check to make sure the heat shields are not banging against the exhaust pipe or cat. My buddy had the same problem, only made noise when he was driving not stopped.