I have a annoying rattle under the dash somewhere what I am wondering is if any one else has this nuisance going on. I am also hesitant to take the top of the dash out but that might be my only solution to figure it out.

Its in my 94z28 m6 . It seems to rattle at idle the most maybe I should just turn the radio up..

 

Rattles can be very difficult sometimes to track down. Try using a piece of tube or hose and stick up to your ear and then the other end poke around under the dash when its rattling to determine the area where its at. Luckily it sounds like yours does it while the car is not moving, otherwise you need a driver while you stand on your head listening around the dash. There are several key support areas/brackets under it, removing the dash pad and the front faces are probably the only way to get to them. May also try spraying some WD40 up in some of the areas hopefully getting some oil on the problem area and quit it down too.

I had to do this with a rattle on the rear part of the car, mine was a convertible so I had my wife drive around slowly on back roads with the top down while I hung over the trunk lid listening around...found the problem to be the carbon canister behind the rear fender well.

 

Can you feel the rattle in the steering wheel? Is it like a resonating vibration?

So, the engine causes it just by idling?

 

I cant feel it through the sterrring wheel but it resonates through the dash. It sounds like a bunch of plastic rattling..

 

If it's coming from the side of the dash, you can remove the roof pillar molding (for access), and stuff some foam in there. I did that because one side was a little low, but I'd imagine it could also help remedy some rattles.