Do you open/close this door a lot? If so, perhaps the weather seal has collapsed a bit and the door can move a bit when you drive. It is very easy to adjust the door's 'strike' located on the body. Slightly loosen the 2 torx head fasteners with a T40 socket (available at most auto parts places and at Sears). Attach masking tape to the door jamb along the top and bottom of the strike to mark the path, and move the 'strike' inward about 1/16", being careful to keep the 'strikes' top and bottom within the guide lines established by the tape. Tighten the T40s and see if this takes cars of the problem.
regards,
Mark