CAT Rattling

[Marty]

hello, so im new to forum had my S8D2 for about 2wks, what started out like a tiny rattle which I thought was a loose heatshield turns out to be my CATs. The previous owner told me he had issues with the CATs and they were "removed" looking underneath, a frankenstein job has been done, opening up the CATs and rewelding them back up.

Im thinking I have two options:
1 - buy new CATs and get an exhuast fabrication shop to fabricate the exhuast section between the downpipes and the mid-section exhaust
2 - just fabricate a straight through pipe removing the CATs? could be issue with MOT?

Any experience / advice welcome.

thanks Marty

[steamship]

Originally Posted by Marty

2 - just fabricate a straight through pipe removing the CATs? could be issue with MOT?

Any changes to the emissions control on a car is an automatic MOT failure. As for the first part of your question, there are members here who have fitted sports CATs to their cars, as the OEM ones are either NLA or very expensive. It might be worth a search to give you some ideas.

[Simon Wallwork]

I had this.
Andy at A for Audi in Glasgow solved it in one second by smacking the rattly cat with a hammer.

[The_Laird]

My cats have been rattling for years. You can’t hear them from inside the car, so it doesn’t bother me. My previous S8 (now with David’S8) had aftermarket sports cats fitted and I know there have been some minor issues with the O2 sensors triggering the engine management light occasionally. I think (??) this can be resolved if some sort of spacer is fitted between the exhaust and the sensor. David is in France just now, so he might not reply quickly.