I've had it since 2001 GF, it's quite severe in my case.I get the 'ringing' or tone changes from time to time...the worse, more constant symptom I get is the white noise sound, like an old cassette tape player in between songs.(hissing)
For me...it's part of having severe TMD, a jaw/muscle malfunction.The tinnitus started right when the TMD hit, so I know that they're intertwined.Simple teeth grinding can cause this.When I used to wear a splint at night I noticed that the tinnitus would be better or worse the next day.Talk to your dentist...if you have a slight overbite or an unusual occlusional process, the tinnitus can be part of this.
*I've also been in 6 car accidents and over 50 fights...both winning and losing.So lots of head trauma in my case
Also you may have damaged the tympanic (?) structure within your ear.In that event a doctor will have to take a look.
Like others here mention, I have very sensitive hearing too.Reading or being in a quiet environment always allows you to hear the sound...for the most part (if it's minor and not structural damage within your ear) it's only blood you're hearing moving through your head.