Tinnitus -- pronounced tih-NITE-us or TIN-uh-tus -- is a condition in which you hear a ringing sound or other noises in one or both ears that no one else hears. The condition is considered common, with the American Tinnitus Association estimating it affects 25 million Americans or about 15 to 20 percent of the population.

According to experts, damage to these hair cells -- by acoustic trauma, allergy, medications, or head trauma -- can cause the brain's circuits not to receive the signals they expect. This causes abnormal neural activity, resulting in the subjective perception of sounds, or tinnitus.

Next, you may be referred to an ear, nose, and throat (ENT) doctor. The ENT will examine your head, neck, and ears and likely have an audiologist test your hearing.

Shatner described an audiometer test that identified the sound of his tinnitus. He said, "And when [the audiometer] reached the same timbre and tone of my sound, I broke into tears. Somebody had hacked their way through this jungle of sound where I was totally alone in my agony, and somebody had reached me. And it just moved me to tears."