Ok, I searched the forum, but seriously, finding this particular noise has been impossible. You know how you take a thick blade of grass and stretch it tight between your thumbs, and then blow on it? Or maybe a plastic wrapper off cheap candy? That's the sound it makes. Kinda like a high-pitched kazoo. It's a whine/squeal. Air induced. It only happens at 65mph+, and of course, intermittently. It immediately goes away when I crack the window. It sounds like it's coming from the passenger side dashboard behind the air vent. Changing the A/C controls, fan speed, recirc/fresh air has no effect.
It is a 2001 Legacy Wagon. 67K miles. Manual.
Edit: I also have a 1990 Loyale with 212,000 miles on it that is my daily driver. Though I am a "noobinator" to the forum please show some respect .