Catalytic converter noise

Hey all, I know that the noise is coming from the busted honeycomb, but are there any theories as to what causes the initial failure of the honeycomb in the catalytic converter? Is it related to gas, new formulations, driving style? I am curious as to the cause since I may replace due to the noise (on my own dime), but want to know if it is something that can be avoided, or from judging by some posts happens fairly regularly? If it happens regularly I will just put up with the annoying noise and save the expense. For those that have replaced OEM and paid for it, what was the cost? I am not really interested in sport cats either, because I live in CA and need to smog the vehicle from time to time, and do not want to go through the process of switching them out. Also will a busted honeycomb cause me not to pass smog in CA? I hav never had a CEL show because of it. Sorry for the ramble... Thanks for any feedback you may have.

What year is your car? I had mine replaced last month under the 8 year/80K federal emissions warranty. The rattle was rally annoying, consider a nice aftermarket exhaust if you have to replace on your dime.

It is a 1999 with 47K so it is out of warranty, exhaust will also be a consideration while everything is out.

I have a pair for sale, they are over $1000 each at the dealership. I think like $1400 or something like that.

good excuse to get a 200 cell cat...

Quotes source post: 7000924

yes!

Noise depends on how the internals "broke." Did they disintegrate into many pieces? Did the honeycomb melt into a block that's rattling around? If you hit the cat with a rubber mallet, you might be able to tell which. Disintegration can be caused by thermal shock (snow or cold water on hot converter), mechanical distortion, or a few other things. Melting usually ends up restricting the exhaust so much that the car bogs. It doesn't sound like you have that. All that said, without a CEL, are you sure you have a busted cat? I don't know CA smog tests, but an inefficient cat should kick off the CEL due to inappropriate secondary oxygen sensor response. Cost at dealer is about $1350 each.

Thanks for the responses...67FJ45 no bogging, sounds more like the disintegration. Positive it is a busted cat. I thought the no cel was weird as well. Thanks for the pricing. I'll post what I end up doing in a month or so.

Mine threw no CEL.. just an awful rattle at idle. My local dealer wanted 2300 bucks to replace ONE cat! thieves! They looked so disappointed when I told them it was covered under warranty. They even argued with me that it was not. Nice eh?

Well, I suppose a disintegrated honeycomb could still be chemically efficient. The exhaust still has to go through the catalyst. Mark, so assuming they were going to charge you, say, $1500 for the part (tax included), that means the dealer was going to charge you $800 for labor. I can switch between my aftermarket and factory cats in about four hours, which includes removing the fascia and bumper. Presumably the dealer could do it faster. Maybe they planned to replace the O2 sensors, too (about $65 each, as I recall). Even so, $2300 for one cat is ridiculous.

Quotes source post: 7003050

They did not even pull the bumper, I asked them if they had to and was told no. When I was picking my car up some guy was collecting his 99 996, they had put a new coolant overflow in, his bill was $1600 if I recall.