Sorry, it is a 1998 E320. I found the problem this morning. The bracket that joins the exhaust pipes between the cat and the muffler had rusted and broken loose causing the pipes to rattle. The quick fix was to bend the bracket up a little to give it clearance. Problem fixed. I am in Tennessee and the car is from Cleveland, OH. These cars do not take the "rust belt" very well(i.e. spring perches, body panels, exhaust system). They will rust if not properly cared for.
The cats are still good, knock on wood!