Had the same issue on the right side….rattle/clicking at highway speeds and worse driving into the wind. Had to different Ford dealers look at it with no results. Thank goodness for this forum! Thanks to the responses I found that the felt cover on the under body of the car has a loose connection right under the driver’s side post between the driver’s door and the passenger door. Remove the cheap plastic connector and replaced with (I believe) a 7mm coarse threaded nut and a large washer. There is no noise now! We were very close to trading it in for another vehicle.