Tinnitus...

Tinnitus comes from the Latin word for "ringing" and is the perception of sound in the human ear in the absence of corresponding external sound(s).

Tinnitus can be perceived in one or both ears or in the head. It is usually described as a ringing noise, but in some patients it takes the form of a high pitched whining, buzzing, hissing, humming, or whistling sound, or as ticking, clicking, roaring, "crickets" or "locusts", tunes, songs, or beeping.  It has also been described as a "whooshing" sound, as of wind or waves.

Symptom

Tinnitus is not itself a disease but a symptom resulting from a range of underlying causes, including ear infections, foreign objects or wax in the ear, and injury from loud noises. Tinnitus is also a side-effect of some oral medications, such as aspirin, and may also result from an abnormally low level of serotonin activity.

The sound perceived may range from a quiet background noise to a signal loud enough to drown out all outside sounds. The term "tinnitus" usually refers to more severe cases. Heller and Bergman (1953) conducted a study of 80 tinnitus-free university students placed in a soundproofed room found that 93% reported hearing a buzzing, pulsing or whistling sound.

Studies have demonstrated that damage to hearing (among other health effects) from unnatural levels of noise exposure is very widespread in industrialized countries.

Because tinnitus is often defined as a subjective phenomenon, it is difficult to measure using objective tests, such as by comparison to noise of known frequency and intensity, as in an audiometric test. The condition is often rated clinically on a simple scale from "slight" to "catastrophic" according to the practical difficulties it imposes, such as interference with sleep, quiet activities, or normal daily activities. 

For research purposes, the more elaborate Tinnitus Handicap Inventory is often used.

Objective tinnitus

In a minority of cases, a clinician can perceive an actual sound emanating from the patient's ears. This is called objective tinnitus.

Objective tinnitus can arise from muscle spasms that cause clicks or crackling around the middle ear. Some people experience a sound that beats in time with the pulse (pulsatile tinnitus). Pulsatile tinnitus is usually objective in nature, resulting from altered blood flow or increased blood turbulence near the ear (such as from atherosclerosis or venous hum), but it can also arise as a subjective phenomenon from an increased awareness of blood flow in the ear. Rarely, pulsatile tinnitus may be a symptom of potentially life-threatening conditions such as carotid artery aneurysm or dissection.