Hi Guys, think I've found a solution to the problem. I started to develop the same noise in my z. First was time I noticed was up/down steep driveways at around 5000km and then more recently the noise started appearing on bumpy roads at around 10000km. If you look at the base of the windscreen whilst outside the car you'll notice a plastic strip running across its base. This plastic strip catches dust and grit underneath, and over time (if not cleaned), the grit will manifest itself as a creaking sounds in the cabin. Try pressing along that plastic strip you'll most likely hear the sounds you've been hearing inside the car.
If you run a high pressure hose along the base of the windscreen, focusing on getting the water under the plastic strip, you will clear any grit/dust from between the strip and windscreen. The end result is no more creaks. Enjoy
