I would second the idea to check the mounting points of any shields on the exhaust system. While the exhaust pipes tend to last a long time, whatever fasteners they use on those shields tend to rust away in about 10 years. Both of our cars have had this issue, and I've had to secure a couple of friends & relatives heatshields over the years too. So far, our moho hasn't been a problem here...yet.
If the shields all seem to be mounted securely, then I guess it is the cat converters. Your rig is about the same year as ours. How many miles on yours? So far, ours still look (and sound) solid. But, we've only got about 45,000 miles on it (I think?).
The cats should last a long, long time, so you might want to follow
theoldwizard1's advice and do some investigating to make sure the engine is running properly.
Good Luck, and be sure to let us know how you make out.
~Rick
2005 Georgie Boy Cruise Master 3625 DS on a Workhorse W-22
Rick, Gail, 1 girl (27-Angel since 2008), 1 girl (22), 2 boys (23 & 20).
2001 Honda Odyssey, Demco Aluminator tow bar & tow plate, SMI Silent Partner brake controller.