[koreth1]

Same experience. When I was a little kid, I thought the high-pitched whine was just what “silence” sounded like.

[subroutine]

My wild hair theory is that it could be due to sleeping with a fan on every night. Looking back, it seems like I always had a box fan, oscillating fan, or ceiling fan running at night. So that's 8 hours of auditory exposure to the same constant frequencies, every night for many years.