Need your input - S8 undercar rattle
 

2002 S8 with 110k Km on the clock.
Symptoms. No issues on cold engine. However, on hot engine I have a undercar rattle that varies with RPM. No errors, loss of effect or CEL.
I will try to be spesific: Car sounds like a diesel but sound is not from front of car, more from under it.

Included a clip that hopefully can help you to help me.

Is this a bad Catalytic Converter or something else?

Thanks in advance

Yggdrasil

Manual link to video: http://www.youtube.com/watch?v=atrP4FFVHAE

loose exhaust heat shield somewhere? Had this on an old Scooby that only manifested itself when hot, as the metal expanded.

Zip

welcome from norway to the uk.
well video sounds bad and since im a pessimist i would say crankshaft bearings or gearbox are finished.
can we see some more interior pics , as im looking into audi exclusive interiors at the moment, and have about 100 different leather pics.

It could be the cats... Difficult to tell, I guess the acoustics in a garage are different to what it would sound outside. It sounded a bit throaty in a nice way, but didnt hear enough of the rattle really....


.. and yes, the interior looked nice as you panned across it at light speed... more more... +++

I'm probably totally wrong here, but a few years back I had a car that had similar symptoms and it turned out to be a cracked torque converter plate

Update on how this "rattle" story ended.
 

Just an update on how this story ended.

After further driving it became very obvious that something the catalytic converter closest to engine made the rattling sound. The porcelain(?) inside of the cat was being crushed into smaller and smaller parts and would eventually clog the whole exhaust pipe. This would be a bad thing if engine was running at high RPM’s.
An exhaust specialist used a simple detection method: Standing under the car (on lift) we looked at the Catalytic converter. It has two “chambers” where the mesh is located easily detectable from outside. He then simply tapped with his knuckle on the chambers and the difference in sound was obvious and identical to what to expect when tapping on a wall for finding cavities.

It was impossible within my timeframe to go for aftermarked. Re-used was not an option as this is a very rare car in Norway. Probably less than 50facelift (of approx. 4 million cars in country) exist due to stupid taxation of engine size and power
Unfortunately sourcing an original CAT from audi was close to impossible. The stealership claimed that there was no OEM NS cat anywhere in Europe and that a new one had to be made with a very long lead time:p. A local highly skilled Audi tuning specialist managed to source up a cat from Germany in two weeks and I had it changed. This was expensive, but I survived and can continue to enjoy the S8.

So, there you have the full story. The CAT was the culprit. Thanks to all that helped me with advice in time of despair. +++

Kind Regards
Yggdrasil

A bit late now, I know, but I recently had 2 sports cats fitted to my 2002 S8 - much cheaper than from Audi and a few more BHP.

There are photos on here somewhere

One of my cats is making exactly the same noise (As of this morning) but at 149,000 miles I can't really complain.

What did your sports cats cost as a pair?

IIRC around £400 for the pair fitted

That's ideal.

Did you go for 200 cell cat's?