10 year (I thought it was 8 years, or 100,00 miles?) on emissions stuff pertains to OE equipped, not aftermarket. And yes, OEM cats are a lot better built than aftermarket ones because they HAVE to last the warranty period - they have durability built-in. This is why they are so much more expensive than aftermarket ones. When I worked for Dynomax/Walker (Tenneco) back in the late 90's-2001, our aftermarket cats were warrantied for 2 years. To the OP & the rattling, the brick(s) inside the cat got loose because the padding broke-down or the brick was never seated correctly when canned, OR the converter was not brought up to temp fully & the foam padding never expanded & seated. This is pretty important to do on new cats - to let them get good & hot for a while so the bricks can seat. As far as aftermarket cats that are 50-state legal, I believe the only ones that are CARB approved are Magnaflow. That's because Magnaflow ponied-up the big $$$ to gain the certification. Cost them a lot of $$ for each part # to gain CARB certification - they are not built any better or different than other brands I'm sure. It's all about the $$. For diesel trucks, including Peterbilts, Freightliners, etc., there is NO CARB-certified aftermarket DPF available, because the manufacturers have all refused to pay California the ridiculous amount per part# to gain the certification! I think it's around $50,000 per part#.

This, all in a nutshell..............

 

Good Info...Thanks^^^^^

I have a magnaflow X pipe on my 94 Mustang GT Convertible with 2 pre cats and 2 high flow magnaflow cats and yes it was a pricey part with the cats BUT much better design and flow than the ford OEM H pipe with the 4 OEM cats.....I will never drive big miles with these cats so not concerned about longevity but read on....

As for longevity, my 2001 Grand prix has 225,000 miles on the OEM cat and it still is functioning correctly and I also have a 08 Chrysler 300 with both cats still functioning correctly at 165,000 miles on them.....I know people with over 300,000 miles on Ford, Chrysler, and GM cats still functioning correctly......

 

GM had issues in the 90's with the cats. My son had a late 90's Regal that started having issues shifting. Turned out to be the cat had disintegrated. Fortunately, it was 58,000 miles - the warranty then was 60,000. It was a $600 fix but was covered. My guess is GM paid for a lot of these and decided it was cheaper to just make them right in the first place.

As for having one on my '80 vette, the original one is in the basement ready to go on if ever needed. So, far no inspector has griped. Since most mechanics are younger than the car they aren't certain what was on it. When I go to dual exhaust sometime in the next 2 years, I'll put a couple cheap ones on.

 

Yes the OE's do have problems with the cats too! It's usually a padding problem - the ceramic bricks are mostly made by Owens Corning & they typically will not go bad by themself - they are totally static. Anyway, when a bunch of OE cats go "bad" - it will either be the padding or the canning. THOSE companies will eat the bad converters, not GM, Ford, Chrysler, etc. The two big OE exhaust manufacturers are still Walker & Arvin (I believe Arvin is still one of the big players). I know for sure Walker is huge OE still. The converters are however made by different companies for the most part, then shipped to Walker & Arvin to weld into the rest of the systems.