I have had this subtle "rattle" from under my car for a few months. Initially my mechanic rewelded my heat shield thinking this was the problem but it persisted. On closer inspection he tells me the cats themselves have a slight rattle. I find this odd in a car with 87K highway miles.

At this point I have no reason to do anything as it is a mild sound, no effect on power and more of an annoyance if anything.

The major question is, in pricing replacement converters, for this older car with 87K miles am I "required" to use C.A.R.B compliant cats as replacements if it gets to that?

Thanks!!

 

If you're in California, then yes. You technically need CARB compliant cats. But depending on where you get your smog test done, they may not notice the difference between OEM and aftermarket cats.

 

I have a rattle on my stock passenger side cat. I have more miles on mine but if you pull the cat it's possible the honeycomb inside it is loose and moving back and forth. Only thing I know can be done is change the cat. Unless you want to knock the honeycomb out. Then you deal with the smell and a check engine light.

 

I had a similar issue, the issue was the metallic honeycomb material after the 02 sensor in the cat separated from the housing. I replaced the cats with Fast Intentions HFC's and don't have any check engine light issues.