What exactly is Tinnitus?
Although tinnitus is usually described as a ringing in the ear, there's a whole range of tunes, buzzes, whooshing sounds, humming and hissing sounds that are described of as tinnitus. The sounds can either genuinely be there or be perceived to be there. If it is genuinely there it suggests muscles ate at play or some blood vessel disease if the sounds are in time with your pulse, but usually its the latter perceived to be there that presents. 

Tinnitus that is perceived and permanent usually suggests damage to your hearing nerve (called the auditory nerve or cranial nerve 8 or vestibulocochlear nerve). The common cause for this we see is patients that have been exposed to loud noises or drugs like certain strong antibiotics which cause damage to the nerve. Other drugs also have a side effect of causing tinnitus. However any ear problems really may cause tinnitus including ear infections, too much wax, getting older, a disease called Mennieres, tumours, neurological diseases, vitamin deficiencies and lots more. 

If you're really interested, keep reading. There's a number of reasons why it might occur. Usually patients presenting with it have some degree of hearing loss. Its thought that somewhere along the line the structures are getting more sensitive to sound because through a feedback mechanism. Think of it this way, you speak to someone but they can't hear you so you speak louder and louder until they can. In the same way its thought that the sensitivity is increased and increased to try to restore hearing but the result is audible nonsense sound from abnormal activity i.e. tinnitus. 

If anything doesn't make sense, please do say :)