Try something for me. Just barely close the rear door and the front door so neither of them are shut tight and go for a short ride. I had a similar sound that was caused by the rear door panel rubbing on the trim when fully closed.
That worked. What did you do to fix it?
Shoulda bought a SCREW...
Sometimes I wish I did. But then I remember a SCREW is just a regular F150 crew cab with fenders and suspension . All jokes aside I like that the SCAB is one of the only extra cab short bed trucks produced. And the SCAB just barely fits in my garage.