How far are you from your dealership? This is something you should reasonably expect them to do for you. If you were my customer, I'd be calling you right now to bring the car in and have one of our techs resolve it for you.
I did take it in to the dealership to fix a rattle. They took the door panel off and installed an insulator pad. Got the car back and can still hear a rattle but not as bad as it was. So now, I figured I could install the dynamat myself. Don't feel like taking it back to the dealer and not fixing it completely.
I've been pushing on everything on that door panel. I even slid a mouse pad down the seal between the door and door panel to try to rid the noise. Worked for a week or so then the noise came back.
I really think it is coming from the inner part of the door panel just above the red, the bigger top part of the panel. If I could get the panel off I could really check and see I'd there is something loose.
If you guys would like a DIY of how to remove the door panel, someone just has to bring one by my place and I'll take it off
Usually to remove door panels on these vehicles, you have to remove all the screws (which are hidden), then pop off the panel (there are plastic rivets holding it on). To find hidden screws you need to look for small trim pieces that can be removed with a interior tool or non sharp screw driver (I am not responsible if you damage anything). After that you can take a look behind the door and shake it a little to try and find rattles. I've done this on most of my cars looking for annoying sounds.
I'm not sure, but its possible that the rattle is coming from the top left shoulder of the seatbelt plastic. the door trim, be careful. there are some screws and mostly clips. refer to previous infiniti models in other forums for diy instructions. are you sure the rattle is from the door panel though? if it is, dynomat would probably be your best solution, but I doubt it.