OK, I took the cowling off and inspected the issue with this problem. The removal is fairly straight forward. Remove the wiper arms, remove the 2 plastic pins on each of the cowling. Release the tabs on the lower front edge of the cowling so it can be lifted up slightly. When the tabs clear the metal base, pull the cowling forward and downward at the same time and it will slide off the lower edge of the windshield. Yes its attached to the lower edge of the windshield. That's where the rub comes in....literally. The plastic tabs that slide up on the windshield are supposed to have felt covering them. In time that felt wears off and the hard plastic rest against the windshield. On mine several of these tabs had the felt either partially missing or missing altogether. This allows the hard plastic to tap against the windshield when bumps are hit in the road, or when the frame flexes enough to cause movement.
The fix has been shown by another posting. Take some sticky backed foam rubber about 1/8" think and fold it over the lower edge of the windshield the full length and this should cure the problem. The foam rubber needs to be about 1/2" wide to wrap around the backside of the glass, over the edge and on the front side of the glass.
I just noticed that creeking noise (FUSTRATING!!!) coming from what I think is the bottom of the passenger side windsheld on my 2013 xB.
bought it in June and this is the first of our cold weather. All the threads on this make sence. I will add a piece of weatherstrip to the bottom of the wiper cowel hopefully this will work.
GREAT SITE love the forums!