In order to get my 92 to pass smog I had to have a new cat put in it and recently I've noticed at times that the exhaust sounds like it's rattling like crazy. I can't seem to figure out what it could be. It's really intermitent as well. Thanks!

 

dude, it's ur muffler bearing

lol, j/k. Check all the points where it mounts to the body, if there is no "bushing" of any kind, there will be intermittant rattling. Otherwise check if it comes anywhere near the body. The cat is the closest thing to the body, while sitting in the car (if it does it while sitting still, if not grab a passenger), have someone stick their head as close to the floor as possible to try and pin point where it's rattling, start by the cat and trace it to the back area.

Also check by the front frame rails, haven't heard of it all too often but the frame rails are relativlely close to the exhaust pipes, not that changing a cat should do that, but also one more area to check.

 

The only time I have ever heard it is when the car is sitting still and it does sound like it's coming from the left rear but I could be wrong.

Would the cat heat sheild also possibly cause this noise?

 

Changing the cat can change how the pipes are in relation to the exhaust sheilds and the frame rails nearby if its slightly longer or shorter than the stock unit. Check all the clearances and move the exhaust around to see if you can hear any rattles. Its probably coming into contact with something nearby. Its also possible for the cat to make noise as well if the brick is loose or one of the sheilds is loose.