Long story short, I came by my tinnitus by way of having a 155 shell strapped to 4 propane tanks detonated under me (IED). Fit for full duty now apart from being a little deaf, ringing, and migraines. For me I have to have noise - can't sleep without a noisy fan in the room, etc. The telemedicine folks said that its because the acoustic chamber in my head is out of factory spec, so as sound waves come in, they're not dampened properly, so they keep bouncing around, and you get the ringing. The right wavelength of noise can counteract to some degree, and mask the ringing, which actually makes it sound quiet - its just 2 noises cancelling each other out, like those noise cancelling headphones.