I have a 2002 Chevrolet Tracker, which has been pretty dependable, although I usually only use it around the state, particularly going up to the camp, since my wife doesn't like me taking her car off-road. We did use it to go to Virginia and back not long ago, though. On the way back, I noticed a rattle and couldn't tell where it was coming from. To me, it sounded like it was coming from the back somewhere, and my wife thought was coming from the front, and neither of us could figure out what it was. I would hear it on acceleration. I brought it in when we got back, and he told me that my catalytic converter had broken. He said also, that they made an after-market catalytic converter that could be used but that they weren't allowed to install them in Maine. The alternative was at a cost of a few hundred dollars. He told me that if it were his car, he'd ignore it and hope that the pieces were small enough to not block my exhaust. If it were blocked, he said there could be a complete loss of power, but more likely it would break up into smaller pieces that would drop off without trouble. This wasn't California, he said, and no state cop was going to crawl under the car to check it. Before he became a mechanic, he was a state cop so I figure he knows that. Well, I have been driving for a couple of weeks now and I don't hear the rattle anymore, and it still runs fine, so I guess I now have a Tracker without a catalytic converter. When they first started requiring them in California, people who knew how to do so were removing them, so I don't guess it's going to do me any harm.
I don't know why the converter would rattle unless it was truly broken, in which case you might be getting fumes into the passenger area. I have had the heat shield get loose that keeps the heat produced by the converter away from the structure of the vehicle. Maybe the shield fell off? Maybe the mechanics here can give you a better answer.
He is a mechanic. He said it was broken and in pieces. There is no smoke in the passenger area or elsewhere. I think that would happen only if it plugged the exhaust, which was the concern.
If it is completely clogged it would stop a vehicle. However, it sounds like the core has crumbled. Drive on and avoid any emission testing area. Should be easy as long as you avoid the left coast. lol
The guy who told me to drive on is the one who does the inspections each year, so I think I'll be good.