Mine is with me like an ever-present 'friend' ... aeroplane and helicopter noise (mostly with helmet and foam earplugs in) has been the ongoing factor, but at various times loud amplifiers and a couple of shooting incidents could have caused some trauma too.
It's workable, not that annoying (maybe because I don't notice it so much these days) but makes the aviation medical beep test a 'guess which ringing tone is real' game rather than a clear-cut experience.