For me it's an attention issue. I went for a checkup and it was a first time I've been in silenced cabin where doctor checks hearing. And I wasn't able to hear some of the frequencies, because of ringing in my ears, which was louder. And doctor expressed some concern about it.

Before that I rarely ever noticed it. Now it is very loud and constant. Maybe it was like that for a long-long time, but now I just focus on it too much.