Tinnitus (pronounced tin – I – tes) is the medical term for the perception of sound when no external sound is present. It is often referred to as “ringing in the ears,” although some people hear hissing, roaring, whistling, chirping, or clicking. Tinnitus can be intermittent or constant-with single or multiple tones-and its perceived volume can range from subtle to shattering. The exact physiological cause or causes of tinnitus are not known. There are, however, several likely sources, all of which are known contributors to tinnitus: noise-induced hearing loss, wax build-up in the ear canal, certain medications, ear or sinus infections, jaw misalignment, cardiovascular disease, certain types of tumors, thyroid disorders, and head and neck trauma. Of these factors, exposure to loud noises is by far the most probable cause of tinnitus. Up to 90 percent of all tinnitus patients have some level of noise-induced hearing loss.