There are two basic causes of ringing in the ears.

1) the nerves are damaged, from blows to the head, viral illness (my left ear suspected damage from measles), or from toxins, or long term exposure to loud sounds.

2) the circulation to the ears may be poor due to inflamed or clogged blood vessels.

Some people use antioxidants for improving the circulation to the ears. There is even a product advertised for it called LipoFlavinoid.
http://www.tinnitusreviews.net/lipoflavinoids.php

Grapeseed extract will also work, and you might try a quality high absorption curcumin as well.

Increasing blood flow to the ear may work, and the amino acid l-arginine is one way to improve blood flow.

Some drugs cause tinnitus too, aspirin, NSAIDs, and caffeine (does it for me).

You might want to check your blood pressure when the tinnitus is loud. High blood pressure is not good for small vessels, in the eye and ear.

Chronic exposure to loud noises, gun discharges, airports can damage the ears permanently. The little fine hair sensors in the inner ear are easily broken.

I've had reduced hearing and poor balance in my left ear since childhood. I had a test called the electronystagmagram, done in my 20's showing the damage. At that time the doctors said...measles or other viral infection or a blow to the head...from my abusive childhood. I can still hear out of it, but my balance is poor because of it. It has very loud tinnitus at times and other times it is quiet. I never connected it to my PN because it has always been with me...the PN came 30 yrs later.