Tinnitus \ tin-night'-is or tin'-it-is (either pronunciation is correct)\ n. [L., tinnire to ring]:
The perception of ringing, hissing, or other sound in the ears or head when no external sound is present. For some people, tinnitus is just a nuisance. For others, it is a life-altering condition. In the United States, an estimated 12 million people have tinnitus to a distressing degree. - researched link

Known causes:
Whilst there are no known causes for tinnitus, there are many factors that have been associated with tinnitus including headaches, emotional tension, anxiety, high blood pressure, anaemia, catarrh, sinus congestion and fatigue. However, as yet there are no known effective medical treatments for this problem.

Although research suggests that lack of sleep and headaches are common related symptoms which may affect the frequency and degree of tinnitus, all cases of tinnitus tend to vary according to the individual; some people suffer only in one ear, others in both. Some people experience a mild ringing noise, whereas others are troubled by loud, high pitched noises. Even diet has been associated with tinnitus and there are numerous alternatives available for the tinnitus sufferer to explore.