I have it.
The sound is an unpleasant, high pitch.
The cause is unknown; it has been present for as long as I can remember. I have never experienced silence. I can always hear the sound when I focus on it, unless I'm listening to loud music or white noise. In silence, my attention automatically shifts to it, but noisy environment can make me forget about it. This is because the brain doesn't focus on constant sounds in our environment; and since this sound has been constant for over 20 years, my brain doesn't need to focus on it and focuses on other relevant sounds in the environment.
So far, I haven't found anything that alleviates it.
