Can anyone tell me how to remove the center a/c vent?
I have a rattle in there and the vent closes by itself when the air is set to the highest speed.

OK, the spring (it looks like a "^") in the bottom of the center vent needs to be pushed down until it releases the vent unit. Then, there are four tabs that pop into holes that must be forced out by pushing from behind (by reaching in where the MCS unit sits). I also used a plastic putty knife to pry from the front. Then, it just pops free!

(P.S. to remove the radio (MCS): This takes about a minute with the removal "keys". I made my removal keys in about 20 minutes after looking at a picture on ebay and cutting them out of a piece of scrap metal.)

No success, yet, but in prying, pulling, tugging, etc., I've finally seen the thingy that sticks up into the middle vent. It appears as a metal pointed prong or arrow head, in about 3" behind the louvers. It is very difficult to see inside the A/C vent behind the louvers. I don't know yet what kind of tool to use to press it downward to pop it out, but will try today starting with screw drivers and the like. Boy, have I butchered this thing - wonder what a replacement is going to cost me??? Removing the radio has not helped one bit because of the existing metal box surrounding the radio that keeps one from accessing the A/C unit.

Yes, ML320guy's suggestins helped and I'm grateful.
But, one man's ML320 is not exactly like the next man's ML320!
Taking out the radio didn't help one bit. Finally, disabling the little
metal clip (by poking it out) made everthing else a piece of cake.
Knowing the metal clip existed was the most important bit of
information. It was not easy to see to know that it was there and
it was not explained by any entry on forums I've checked. Getting
it out was even more difficult. I was desperate and used a screw
driver to poke the thing out of its location in the center of the A/C
unit. Pictures I have are too large for this site.
my email is bjebre@adelphia.net