I've had a rattle near that A pillar/driver side forward dash area for a few weeks now...ever since having my MFD replaced.
I could get the rattle to go away by pressing hard on the main vent on the left side or by pressing on the forward area of the dash.
So, today, I went out to see if I could stop it, armed with my trusty roll of weather stripping.
Here's what I did and found. First, I took off the silver vent piece thinking that would be the easiest way to get under the black part of the dash without major disassembly. Once that was off I poked on the black part of the dash trying to find where the rattle most likely came from.
I found that I couldn't really reproduce it that way. It was a little loose here and there, but not bad and it seemed adequately padded. But when I tapped near the little triangle window I noticed that the little plastic piece with the vent holes for that tiny little window DID rattle.
I popped it out (very easy, just get under the edge facing the driver and lift up). I strategicly placed a couple of pieces of weather stripping and put it back...tapped...no rattle.
I went a head and put a piece of weather stripping under the edge of the black part of the dash right where the silver vent cover goes b/c it was a little loose.
I also put a piece of weather stripping on the vent cover near each set of tabs (3 total) before putting it back on.
Finally, I took out the center speaker, put a little triangle of weather stripping on each corner of that, unplugged it (some have suggested this improves the stereo seperation, worth a try). I put it back in. Although I haven't had a big problem with it rattling it does on occasion so while in Rome....
I haven't taken her out for a drive yet, but I'm pretty confident that'll do the trick.