I have mild Tinnitus. In the day time i don't notice it at all, but about 6 months back when trying to sleep, i could hear a constant low frequency bass tone a bit like a car engine running outside, or a fridge freezer compressor. Over the course of about 3 months, the low frequency tone turned to a high frequency tone which is constant jet engine noise, and is most noticeable at night when completely silence.
Mine was caused by wearing headphones on my pc. Some songs and in game sounds are are suddenly a lot louder than others and its totally unexpected. That 2 or 3 seconds of intense volume increase over the years have given me this.
Crysis 2 was the latest game to set mine off for the worse. You jump on this lift on the side of a building and it crashes to the ground. Way over the top volume and totally uncalled for, especially when the rest of the game is at a comfortable volume.
Little tip, if you have an asus card, enable the smart volume normaliser. It tries to keep all sources the same volume levels, so no more unexpected frights.