Does the door rattle when you grab the outside handle and jerk it around? If not, take the cardboard cover off and see if the flat rod that goes between the inside door handle and the door latch is making the noise. I have seen where someone has rapped a portion of this part with tape -and I'm guessing- to stop a rattle. I have seen this done on two different AD trucks. Also, check for debris, dropped tools or door parts that fell and ended up in the bottom of the door. A good way to isolate the source of rattles and noises anywhere on a vehicle is to use a rubber mallet and bang around the suspected area.
