FWIW I don't think this sound is saddle related. It has the frequency of a rotational part. That is either the wheels or the drivetrain. Are the tires kept at max pressure or something lower? There is more bulge in sidewalls than when the tire is inflated to max pressure. If the fenders are close clearance the scraping that results would not be unlike what is heard in the video. The sound begins at 4 miles ... so something is heating up. In it's cold, contracted state, it is not a problem. It might be a brake caliper. Hydraulic? If I had the bike in front of me I would find that sound. I am appalled that after $800 spent, pro mechanics can't find it. If it is a brake caliper and you heat it up to the point where it is making noise you have to jump right off and spin stuff to find it. Even a few seconds of delay will allow the part to shrink back to a noiseless state. Finally, is the sound louder in some gear combinations than others? I thought I heard a change in the quality of the sound after a shift. Much longer and better quality videos are needed if any useful help is to be forthcoming. All I have for now.