I had a 1965 Rambler that had a wind noise that would start at 45 mph and go away about 55 mph. The noise was one of the vertical bars in the grille. It didn't bother me, but one of the technicians at the dealer traced it down because it bothered him when he took the car for a test drive for another repair.
If your noise just started, have you done something recently--replaced a light, added or removed a front license or vanity plate, etc.
Another possibility may be the seal around the windshield. I had a rental car once that had such a bad buzzing noise when I reached highway speed that I took it back. The rental agency apologized and explained that the windshield had just been replaced and apparently the job wasn't done correctly. I was given a free upgrade.