My 330i has a slight rattle from the dashboard but more from around the cluster or steering wheel area. The passenger seat has something that rattles lightly when nobody is sitting there, and at the rear there is also something that rattles a bit - don't have roller-blinds so not that which is usually the case. Apparently there is an issue with E90 door seal rubbers that can also cause rattles.
For the PDC, easiest is to have someone walk around behind the car while it is active and see if it is able to sense the presence consistently from various distances between from less than a ruler's distance away from the bumper to say 1.5 metres.