What makes a catalytic converter to rattle?

I have a 1998 Chevy S10, and it's been making a rattling noise for some time. I've been told this is the catalytic converter,so I was wondering, what causes it to make this noise?|||EIther the heat shield on the outside, or the internal components have worn out and pieces have broken off inside. This is usually the result of driving with a misfire problem and fuel going into the exhaust system.|||^^^ this will not cause fuel to go into the exhaust or misfiring.





It may sound like the vehicle is misfiring if there is a hole in the exhaust system. I would bet good money that it's your heat shield that has come lose. You might be able to just tighten it back up if it hasn't rusted through.|||they get old and start to burn out inside and the shell on the outside gets loose. it might even be the heat shield around it rattling.|||a symptom of being worn out.