Great thread. I just did a 700-mile interstate road trip and noticed some drone around 80mph. I hadn't noticed any before but really until now I hadn't been at 80mph for any sustained speed. At first I thought it was an exhaust leak, but this makes more sense since others are experiencing it.
Really at normal speeds it sounds terrific. I suspect even the "quiet" exhausts like Cobb and Mountune are going to have some drone at such speeds. However since I don't travel that far or at that speed for a sustained period of time often it's no big deal.