If you have tinnitus, then the best noice-cancelling method is to introduce white noise. White noise is the sort of noise where the amplitude is equal on all the wavelenghts, and there are actually many commercial tinnitus blockers out there (i know this stuff because my parents are into it, hehe (i knew it would come in handy some day)).
The way to produce white noise at home is to grab a radio and tune it somewhere between the stations (a tv would do too, but i suppose that the "snow" on the screen could be a little disturbing). The static noise you hear is very close to the ideal white noise. Now, you should turn the volume down until you barely hear it, and it still has to be louder than the ringing.
Now, this all will work IF it's tinnitus, and the best idea would be to go to a doctor and ask for their advice (i'm not a doctor
) I think they can even measure the intensity of ringing that you hear...
p.s. I hope my answer doesn't come in WAY too late