My 99 2500 V10 has a rattling sound at around 2000 RPM, when the load is light or between shifts. Sounds like valve train noise to me. As I looked on line for ideas on this i found many of the same noise complaints from the catalytic converters. Whats your thoughts on this? Could this rattling noise travel up the head pipes and sound like its in the engine?

I was looking into this noise today in the shop. If i feather the throttle under the hood it sounds like a Diesel. I did crawl under the cats and at idle they are making a metal rattle sound like the insides are falling apart. Anyone ever deal with this?