I have also heard the plastic valance flap around 80-90 mph, i can hear it and sensed where it was coming from. ( You can actually feel it a little) There is not a good fix for this without some sort of a return or sloped edge, even with metal stiffeners you have a dam effect.

Lets see now, overspary on driverside rear rubber window molding, passenger door arm rest leather is not tucked in, bolts in seat, trunk mat doesn't fit, carbon fiber hood stripe needs trim where it rolls under hood