Thanks for posting this. I believe they actually got it right. Today I climbed under my ST and sure enough the underbody panels were loose on both sides, but more so the driver side. There was at least a half inch of space between the panel and the underbody, perfect for wind at high speed to get in and make them vibrate badly. Unfortunately on the outer edges under the B-pillars, there are 2 cheap plastic fasteners and small hanging bolts without nuts. They just put thin fastening washers on the bolts, which once the plastic fasteners come loose just don't hold the panel in place.
So I put nuts and large washers on those bolts, tightened them down, then carefully tightened the plastic fasteners. I then tightened every other existing nut and plastic fastener on the panels all the way to the center of the vehicle. Then on the leading edge corners of the panel where it could vibrate, I adhered thin rubber padding to the underbody above to make it more snug and hopefully more quiet.
I took her out on the interstate and drove her 80+. Happy to say not even a peep out of either side.