I have also had this issue with my xfire. It does not happen every time I close but it does happen every now and then. I may be mistaken but if I recall correctly this issue was covered on a Technical Service Bulletin for the Crossfire. I'm not sure if the issue was ever properly resolved but you might want to check out the TSB's on the crossfire because there is a laundry list of them. I guarantee that most of the tiny little issues you have with the car will be covered on there.

But for now I suggest just messing with the window. Try a little experimentation if you want to. Like, roll the window up and down a few times with the door closed and then open and shut the door to see if anything changes or to see how it reacts. Then roll the window up and down a few times with the door open to see how the door shuts or if it shuts differently that way. Maybe push the rubber molding up around the frame of the door. Just get investigative with it and see if you can locate something before you take it to the dealer again. Good Luck Man!!