05 CDI tin can rattling
 

I was expecting to find a loose heat shield causing the rattling when the engine warms up, but the heat shields are parts attached to the underbody. The source of the tin rattling appears to be coming from inside the catalic converter? I've never heard the internals just wondering if that means time to replace it?

With car off hit it with a rubber mallet. If you hear rattle replace it.

Yes its a faint rattling sound. I searched around but so far only the dealer sells remanufactured cats. Wondering if anyone knows of a cat rebuilder?