I know what it is that is causing the rattling. From what I understand it is common on 4th gens to generate this rattle. I don't know the name of the piece. I think it is the tunnel brace... Anyways, can someone tell me what it's called please? Also, the larger question:what can I do to stop the rattle? Do I need it there? It is stock. It gets really annoying! Please help!

 

Look under the car for something loose.

My 4th Gen exhaust never rattled.

BTW, this isn't a Tech question by far.

 

is it stock exhaust?

id be willing to bet it's a heat shield around the exhaust somewhere. you'll have to look. and that is as easy to fix as bending it out of the way.

and you should be able to see if the pipe is close to the cross brace.

 

Could be the rings around the O2 sensors.

 

I used little pieces of duct tape to solve that problem

Also if the Y pipe is banging the tunnel brace it may be a motor and or trans mount problem.

 

You could also move the tunnel brace down by putting a washer on the bolts between the brace and the floor pan. That should give you an extra 1/8 inch of clearance (depending on how thick of a washer you use). You'll need 4 of them.

On a stock car, this is more of a band-aid instead of a fix if the tunnel brace is truly the issue. As mentioned above, look for worn out motor mounts and loose heat shields as other potential rattling sources. Cat. converters may also rattle on their way out...

 

The heat shields under the passenger seat toward the front on mine rattled, some pliers and a little bending solved the problem.