I've noticed a squeak in my dash (not a rattle) and it seems to go away if I press down on the top of the dash right behind the steering wheel. With that totally unscientific test it seems that the squeak is coming from the dash/instrument cluster bezel (dash face) junction. I have a feeling that if I tighten the face down, or take it out and put some strips of foam back there it should stop the squeak.
Not sure if that is your issue, but I know many of us have been in and out of our dashes a lot and the face may be a little loose, so that may be where your rattle/ squeak is coming from.
"The major difference between a thing that might go wrong and a thing that cannot possibly go wrong is that when a thing that cannot possibly go wrong goes wrong, it usually turns out to be impossible to get at or repair."
-Douglas Adams, Mostly Harmless