Eeh im not sure if this is the same prob i had or not but if u can put ur hand on the center vent (the big one on top of the dash just above the radio) and the rattle goes away it is .... anyways if so theres a DIY for fixing this dash rattle over on vortex i think .... or u could do what i did and replace it with the dash tray that www.oempl.us sells
For the vents on the drivers side, passenger side, and on top of the dash (the large one causing the rattling) you literally have to stick a flat head screw driver in between the dash and the vent and pop it out. It takes a little bit of shoving, but it will come out.
I spent 3 hours looking for a civilized way to get them out. Turns out, you just pry them.
This is on an MKV GTI, by the way.