seems many have experienced this "rattling of sabers" sound when the cat element starts to come apart.

At what mileage did this occur and was it Left/Right that let go?

Lets try to keep it subjective and dealing only with elemental disintegration. Not when you replaced yours to go to a different exhaust or when your downpipe leaked or broke. Lets restrict it to catalyst fragmentation only, see what we get. It may prove eminent to many of us.

Dont know if previous ownder replaced though...

Rattled for about 100 miles and then total blockage, couldn't rev the car past 4k.

that I have heard on other 12V's - even when brand new. I always thought it was from the stock exhaust. But curently, my car has a glasspack, REMUS muffler and no cats and it still does it. Oh yeah, modified manifolds too. Weird. Must be induction produced resonance. I like it though.

rattles at 3000-3500 rpm

and you're the 2nd who's mentioned that rattling sound associated w/2.8's. I have yet to hear it or even any sound that could be close or similar to it. Now I'm VERY curious as surely Audi would've sold a LOT fewer of these were that sound audible on a pre-purchase test drive.

And if it wasn't disceranble on a new car when purchased, what is happening to make it so common on older cars? And it's almost a given that any rattle is (more than likely) metal-to-metal contact, what exactly in the induction system is pre-disposed to originating that sound? Switchover mechanism is the only thing in the intake tract besides TB butterflies that offers any opportunity of metal-to-metal contact.

Any ideas?

...so i did both of them.

started with Karting. Steve was there.

It's not really a sound that would drive people away. In fact it's usually audible when the Audi is driven away and you are listening to it from a distance. Usually mid RPM's at the lower gears. I kinda like the sound, it definitely is distinct and none of my other cars or my folks (including my Sister's 30V Passat) does it.

At first I was thinking it was the cats, but as I said, I don't have them for a while and it still does it. Then maybe it's the heat shields. Well, one side is missing because of my manifold, yet it still sounds the same. So, I figured it's somewhere upstream. It could be the switchover and some turbulence causing resonance, but I dunno. I kinda like it, so whatever I do, I hope I don't loose it

I wish I can get that signature sound of the UR Audi's (5 cylinder) - that is definetely distinct Audi and music :)
It may have to do with altitude, which is why you may not have noticed. Maybe I'll keep a camcorder running to capture a clip one of these days. I have to put my car back to stock next month because smog (emmission) check is due and registration in September. Perfect to have a long 2 years of fun after I bolt a new turbo and new manifold after my wedding next month.

I'm catching up and I see you've been busy! Congrats and great job! Looks like many 12Vers are enjoying new found power thanks to you :)

Got them replaced for free due to the federal law. I also fixed the problem that cause them to fail so prematurely.

Mike

they are, however, gone now so we won't know how long they would have lasted

which was around 159k. I thought it was only the left cat but I'm not sure. My exhaust is like no other I've ever heard. Kind of like a 5.0 with a free flow exhaust except high in pitch and not as loud. Very metallic and raspy sounding. I'm just wondering if it's restricting my flow. My check engine light would come on all the time but rarely comes on now.

every time i leave work, i get into 2nd gear and then i hit the light so i just engine brake to the light and i hear all kinds of noise coming from under the car. I also get that sound when i'm accelerating in 3rd gear when the engine isn't fully warmed up yet...

I'm guessing that's my cat making all that crackling?

btw, i got this somewhere in the 88-90k area sometime, but after i got my coilpacks changed due to idling issues, it went away. but now it's back again.

I don't think that's the cat, but just some some condensation in the exhaust heating up and making popping noises.
I also got a serious problem with exhaust flatulance when coasting downhill, even when the engine and exhaust are hot. No idea about that noise... :D

... and a bad MAF.

Mike