My s8 de-catted itself !!!
 

I came to sell the old O/S cat for scrap along with some others i have to cash in, on trimming the pipes either side of the core, discovered there was no monolith inside !!! It has blown it away lol. I did drive it for quite a few months with that tell tell rattle but then it stopped. Only at the MOT did the problem raise itself as it failed on CO along with a catalyst code on VCDS...

Quite extreme and clean as a whistle on the inside !!

Amazingly smooth round self-decat +++
My S8 has some sort of rattle too I wonder if its the cats, I hope its not the release bearing or something transmission related.

I used to only notice it at lower speeds and on over run if popping the throttle - its quite subtle yet tinny metalic exhaust sound. You can get a mechanics stethoscope to help pin point it but id say the two sounds are quite different

Lol - reminds me of the cat on my BX16v which spat itself out over time! At night you could see bits of it glowing still when it hit the road surface behind me....

My S8 did the same thing whilst I was on my way to get some sports cats fitted. I was driving carefully up the M1. Going through a set of roadworks I had a Merc E-class coming flying behind and sit 10ft off my rear bumper. At the NSL sign I put my foot down, the car kicked down into 3rd and gained speed at a glacial pace, as the monolith was blocking the exhaust and causing huge back pressure. Then with an almighty clunk and rattle it spat the contents of one of the cats out the exhaust, showering the Merc with smoke and metallic particles, so thick you couldn't actually see his car through it. At which point the S8 shot off like a rat with a firework up its arse...

Bah! Typical Merc drivers ;)

Beauty of V8- if one side gets blocked you can still drive. Once I had catalyst brake down on Mondeo. Large chuck broke of it at the front of catalyst and turned sideways blocking exhaust flow. Car could not get above 25mph.