I have exactly the same thing. Most tinnitus is caused damage to the hair cells in the cochlea from loud noises for extended periods of time (as is mine). My theory is that the brain basically turns up the gain to compensate for the poor performance of the sensor. I think tinnitus is basically interference, or cross-talk from other nervous processes that normally are low level background.

Last time I went for a hearing test the doctor asked me if I had been in an explosion (not to my knowledge).