I have a 2000 SS Auto, when i am sitting at a stop light or maybe creeping along i get this really bad kind of rattling sounds from under the car about in the middle. If i put it in neutral at the stop light it stops. I was thinking maybe u-joints but i'm 18 and haven't gotten started on learning how to repair cars yet and I've only had the car a couple months so anybody that has had a similar problem or just knows what it is please help. Corey

 

maybe its the exhaust... and your car just idles better at nuetral...

i have a real soft rattle and that was after i changed my exhaust...

maybe that is it! but don't take my word for it, get more opinions

 

u joints dont turn while your standing still. Check your exaust.

 

Could be something against a heat shield. Try to find a rack ( muffler shop?)
and check it from below. Look for anything loose or against metal. Heat shields make a lot of noise with very little vibration,almost like a bell.