I have a 2000 ram 4x4 sport with the off-road pkg. Its got the 5.9 and recently it has started making a funny vibration. Little history....I recently lost my exhaust due to the fact that it rusted off right behind the cat. I have replaced it with a flow master and dual outlets. While I was doing the exhaust I was thinking about removing or gutting the cat..but I didnt. I did notice while installing the exhaust, I had some rattling in the cat..like the insides where busted up.Anyway...when i am driving say 60-65 and punch it..and let off, I get this wierd sound and vibration..im not sure if its caused by the back pressure rattling the insides of the broken cat or what. The tranny has been rebuilt and when I installed the exhaust I welded all joints so i know its not vibrating....anyone else had anything like this?

 

If the cat was rattling, you should have gutted or replaced it. Then move on to to other diagnostics. Like checking the "plenum" comes to mind.

 

htrod02- I have experienced a similar vibration while driving along the highway also. If I let my foot off the gas pedal, the vibraition (almost like a mud tire humming on pavement) sound appears. I can feather the gas pedal to make the vibration quieter or louder by letting off the gas. I have the cat back exhaust from flowmaster as well. Come to think of it, I had gibson exhaust before and i dont recall this vibration.