Interesting read! I have had my dash replaced as when it was delivered there was a 6 inch long scratch or defect on the passenger side. The dealer replaced it and you would never know but it's going back tomorrow due to a rattle. One was there before the dash was changed but stopped and now started again. It sounds exactly like what you describe. I just checked and the visor certainly makes the thud that I have been hearing. I also have another rattle so hopefully they will sort that!
