I cannot give you a very good answer other than to say that I think you are correct that it is not the lock, latches etc. That doesn't really make sense to me and also if you push/pull on the door and there is no change then that tends to prove it. My 202 has many many rattles all over the place, far too many for me to list here. Some seem temperature dependent, others just come and go. Some, like yours, are maddeningly difficult to locate spatially. Every time I turn my head they seem to be coming from somewhere else. My passengers can't find them either. Since the car is under warranty I would definitly explore that route. There might even be a TSB issued on it. The dealer has special kits to work on rattle complaints. I have identified some of my rattles and not others. Some people will say that their Mercedes never rattles. I have only had this one so I can't say. As far as getting specific advice on your car, you might, but I have found that there is a much larger body of knowledge on this site for the W124's and older cars in general. There are less 202's and 203's around and they are newer. I see questions like this sometimes sit unanswered, and the resident geniuses seem to be scarce lately. Maybe they are on vacation or just tired!

Mike

__________________
1998 C230 330,000 miles (currently dead of second failed EIS, yours will fail too, turning you into the dealer's personal human cash machine)
1988 F150 144,000 miles (leaks all the colors of the rainbow)
Previous stars: 1981 Brava 210,000 miles, 1978 128 150,000 miles, 1977 B200 Van 175,000 miles, 1972 Vega (great, if rusty, car), 1972 Celica, 1986.5 Supra