The guys over in the LS1 section really helped out with some engine performance issues I was having. Now I'm hoping to solve this one last problem.

The car is a 2000 Camaro SS with an automatic transmission.

I have a terrible rattle/vibration coming from under the car. It only happens when I come to a complete stop. Even then, it doesn't always happen. When it does, you can hear it and feel it in the car. If I shift to neutral, the rattle stops.

The problem seems to start shortly after I had the car in for service. I had them change the plugs and wires, since they're so difficult to get to. At the same time, there was some sort of catalytic converter recall, and they took care of that, too. I figured the problem was some loose exhaust pipes that gets to close to something else while the drivetrain is engaged. But I can't find anything under the car that's loose.

What do you think? Does this sound like an exhaust problem? Or could it be a transmission mount or torque converter problem? Since it's intermitant and only happens when the car comes to a stop, I can't find much information online. All the rattle problems I find apply when the car is accelerating, which isn't the case here.

 

From the info given, I'd start by looking at the exhaust. It's not uncommon to have an intermittent rattle, particularly while stopped and in gear. Look at the staped brace on the trans tunnel and see if the intermediate pipe is sitting on or very close to that brace. Also look at the area where the intermediate pipe goes over the axle, as it tends to hit the brace above the panhard bar and/or the body if not adjusted just right. Assuming you still have the stock exhaust, the trans tunnel brace is the more likely culprit, especially if they did work on the passenger side cat.