Tinnitus is caused by damage to nerves in the ear. It manifests itself in many ways so we can't just say it's this or that. Its different for each person.
Ear plugs, muffs, etc can't help it because it's coming from the nerves, not outside the ear. It's not real noise. Plugs might have a placebo effect for a while but they don't stop it. In some people it can be debilitating.
There are treatments to reduce it but it's incurable. The type of treatment that works for any person is highly variable because the problem is so variable.
FWIW, there are 2 ways to pronounce it.
Most of us commoners say tin EYE' tus. Researchers and many doctors call it TINN' itus.
