samething is happening to me i got 99,000 miles and my engine light is on, left cat rattles, lots of shops also declined to fix it only dealer I cant find a cat anywhere for this car Quattro 3.0.

I would repalce the O2 sensor first, but the cats are probably out, dealer told me mine were dead.
So I'm going to remove the cats have an exhaust shop cut them out and put a straight pipe with a hole so you can put the o2 sensor also install o2 simulators so ur light won't come on. And then at the bottom I'll install some high flow ,that way next time it will be easier to replace them.

 

faackkk am i pissed...\

no codes. symptoms were significantly noticeble with power loss and LOUD rattle from the engine at idle. At first i thought cam chain tensioner...told my mechanic to doan oil pressure test he went against my wishes and diagnosed the problem. Didn't phone me and just installed it - dealer, $800+ he installed it for $650...

I read a write up on here about gains with a test pipe + exhaust, wasrediculous #s for me. We have absolutely no emmission restrictions and have always run a straight pipe on all my cars before!