The catalytic converter has a heat shield which may look burned out when the actual converter is not. Of course if it is actually blown out or defective you should do something about that, but if it's the mesh on the bottom that's rotted, it's pretty common.
Your first job will be to try to narrow down what kind of smell it is. As soon as you pull into the garage, you should be prepared to pop the hood open, and look for any wisps of smoke or steam, and to get underneath for the same thing. Possibilities are many. Check underneath for signs of an oil leak, especially at the rear of the engne, where oil can hit the exhaust pipe. It might also be a good idea to have the colling system pressure checked, if you think it might be antifreeze and can't see any traces of leakage.
Also, don't forget that if you regularly pull through a slushy puddle or the like on the way into the garage, the mud on the exahaust can make a strange smell.
