The noise is similar to the well known marble in a can noise that is a feature of the C5 but, much louder. It is occuring all of the time now. Depressing the clutch has no effect either way. It is loudest when the car is idling in neutral and when it is deselerating. I was under the car with it running last night and the noise seems to be the loudest in the center of the car where the catalytic converters are located. It sounds like something has come loose or broken in the torque tube. Any suggestions on how I can diagnose the problem? I believe I will have to remove the torque tube to figure it out. My exhaust is welded to the headers and I'm assuming all of that stuff will need to drop to remove the torque tube. Let me know what you guys think. Thanks.

 

Is there a way that I can test if one of the catalytic converters has gone bad?

 

You need to have your torque tube rebuilt, it doesnt cost that much. It happend to my 99 FRC I thought it was the clutch but after I replaced it I found out I had to take it back apart.
Matt