This article is from the Tinnitus FAQ, by email@example.com (Mark Bixby) with numerous contributions by others.
One possible cause is Diabetes. Other than that no one that I
have spoken with knows. It may also be hereditary. Usually
doesn't show up until later in life 40 and beyond, and can burn
itself out in 3 - 5 years. Some have it earlier in life (me at
35) and could have it the rest of our lives.