When I have my windows down, at around 50+ mph, my passenger seatbelt (the part coming out of the trim, not the shoulder belt) flaps like crazy and it ruins the experience because it's so loud and annoying. Does anyone have any ideas on how to fix this? I'm thinking of somehow fastening a strap to the trim to hold the seatbelt down, but I don't really know.
I have noticed that. You need a left to right cross-wind to make it happen. I roll up the window until I drive in another direction, and then roll it back down. Is your passenger window up or down? I think you can change the window positions to change the air flow and get the belt to quiet down, but it's not easy with crank windows!