Here is a clogged main cat

This is a clogged pre-cat

Cats usually blow out when you are running too rich in your car. If your car is stock, it could be caused by the wrong timing or by leaving your car idle for too long. I had the same issue of the rattling noise coming from my exhaust system when it was cold. After it warmed up, the rattling went away. The rattle was caused by pieces of the cat that were blown out and stuck in the exhaust piping. The best way to find out is to unbolt the exhaust from the main-cat and shine a flashlight in there and see whats going on.

 

Vibration when it's cold eh? I bet that's what's wrong with my daily driver. Are you getting crappy gas mileage too?

 

MrJohnTan , thanks for the information and the pictures. I think I'm starting to figure this out,
- My check engine light came on a couple of months ago but hasn't since then
- I have been getting poor gas mileage which means I'm running rich which could cause the Cat to get clogged which probably also means I have a bad O2 sensor, right?
How did you un-clog your cat? Did you have to replace anything or just clean it out?

 

so Only when u start up?wut about when u drive? dis ur RPM idlin kinda weird?brounce up alilo?

 

I found a used main and precat for sale and swapped them out. My butt dyno says I gained some HP that I lost from the clogged cats.

As for the check engine light, O2 sensor is a possibility. Id try to pull the codes even if it has been a couple of months. If your ECU hasnt been reset since then, chances are the codes may still be in there.