I've been dealing with it for the better part of 25yrs. Too many yrs of chainsaws,woodchippers,hvy construction noises,shooting/hunting,etc. Rocky and others have pretty much covered it all. I will add two other things that make it worse,hearing loss and head congestion(head colds,ear infections,sinus infections/congestion).For me it's allergies and irritants. When the noise(mine is like a high pitched electrical whine)starts to get louder I know the congestion is starting so start meds(across the counter or scrip what ever seems to work at the time). I recently started allergy shots.
My wife works for the WV School For The Deaf And Blind. I've known the audiologist there for many yrs. As she tells me,if there's a cure(operation)or med that helps she'd know or will know of it but to date,nothing. I asked her one time that if I were to go completely deaf if the noise would stop and she said no. She did let me borrow a hearing aid for a month and it really helped by letting normal noise over ride somewhat the tinnitus noise. I registered yrs ago with the Tinnitus Foundation and would periodically gets updates from them but haven't for YRS now.
Guess that's about all I can add other than when it seems to get so bad that you don't know how much more you can take,just remember your not alone in your suffering.