Hi clfrannie. Welcome to the forum. No mechanic should be risking his reputation by destroying an emissions device. In some states that will get you jail time. In most others, it will get you a huge fine. That may have been common practice by HIM but not by professionals. Doing anything like that, or removing a converter in my Auto Shop would have gotten the car instantly removed to the parking lot. A second offense would have gotten the student removed from the program. It was that serious, and we aren't even in an emissions-testing area.
Besides the obvious increase in air pollution, starting with '96 models, the emissions system is generically called On-Board Diagnostics version 2, (OBD2). It is required on all vehicles sold in the U.S. Besides still using the normal oxygen sensor right before the catalytic converter, there is a second one after it to monitor the converter's efficiency. The first one will switch very rapidly between "rich" and "lean". If the converter is doing its job, the second O2 sensor will switch between rich and lean very slowly. When no change in the exhaust gas takes place in the converter, the second sensor will switch just as fast as the first one. That's how the engine computer knows the converter is working.
When an efficiency problem is detected with the converter, the Check Engine light is turned on and a corresponding diagnostic fault code is set. There are many other problems that can be detected and the light will let you know, but if the converter isn't working, the Check Engine light will always be on. That will cause you to not know if an additional, possibly serious problem is occurring.
If you're sure the converter is rattling internally, (you can verify this by banging on it with your fist or a rubber hammer), a simple effective fix is to drill a small hole in the bottom of it, and run in a self-tapping bolt. A license plate bolt is the perfect size, but once the hole is started, before you run it all the way in, grind off the point of the bolt. That will prevent it from digging into the substrate material which will allow it to rattle again in the future. I did this to my '88 Grand Caravan about 15 years ago and it is still quiet.
Tuesday, May 11th, 2010 AT 1:58 PM