Signed up especially to post on this thread!
I have the exact same issue with my car, 07 E92. Flappy, plastic tapping rattle coming from somewhere on the passenger side, which is wind related and only occurs above 60mph. Sometimes silences itself and then only occurs above 70,80 or even 90 (on private track) but always comes back eventually.
I had originally thought it might be the under bonnet insulation or possibly the arch liner, but no dice.
I will be checking this bolt/nut out and will report back!
