So my car has been acting up recently. From time to time my cats will start knocking and rattling, and when that happens, my car would start running a bit poorly. It would seem to have still good low end, but as the car gets going higher in the revs, it seems to have more problems. Then occasionally the cats would stop rattling and the car would seem to run ok. Could bad cats be the cause of my problems. I just checked all my wires, which are new about 2k miles from when my engine war rebuilt, so I don't think that it is a tune up issue, and the car does not have any codes stored. Could clogged cats cause my car to run this poorly and make it idle a bit rough?
The cats are welded on there, and I don't think that I would have a way of knowing what is going on in there without cutting them off.
Any suggestions would be greatly appreciated.

 

Clog cats is a possibility. If you are unsure just replace the cat. Muffler shops can cut and install them for you. I would do a tuneup again even though the engine was rebuilt. knocking and rattling isn't something to push aside. running clean is mean

 

So it did happen to be one bad catalytic converter. The other looked fine, but I think I would replace it in the near future since it could be on its way out.
The bat cat was the one on the left side. It looked as if someone had taken a stick and pushed the honey combs into the exhaust pipe. After the replacing that cat, my car runs so much better. It revs a lot easier, and runs like a raped ape.

 

i had that 6 months back and now it did it again. Looked exactly the same inside

 

Make sure that you don't have any spark plugs that are missing, and also that your O2 sensors are functioning properly. A miss will make your cats go bad in a heart beat.
Also, when you replace your catalytic converter, replace it with a good quality one. I have found that when I spend 50 bucks on a cat, I get what I pay for - garbage.