While I agree that the brain can generally block it out once you accept it, I'll add that sometimes (for some people) it goes from a constant tone to intermittent chirping. The first time mine layered in a "typewriter tinnitus"[1] I wondered if I was picking up electronic interference in my head, which is a bit more difficult to tune out.

[1] https://youtu.be/bWPuYol1Tjo