@Owen, how often have new sounds appeared for you? Has it ever slowed down, or do they just keep appearing?
I'm not sure the cause of your tinnitus, but I've been told by an audiologist and 2 different ENTs that for those that have tinnitus as a consequence of causes other than noise induced, their experience suggests that the progression is significantly less predictable as it is less clear what damage has been caused - either permanent or temporary.
Tinnitus took about a year to develop after I started taking Levothyroxine, with a second noise added after about 3 months and a third after a further 3 months. Initially a roar, then Morse code and finally a ring.
No new ones developed over the next 6 months, but those I had already, became louder and louder until they were almost deafening.
Then, new noises generally appeared every 3-4 weeks over the course of the next 6-8 months after I moved from Levothyroxine to NDT, but the overall amplitude started to reduce.
I seem to have developed just 1 new one over the last 2 months and I have noticed that the number of sounds has gone down to around 6 over the past month.
I still remain optimistic that they will continue to become quieter as time goes on. I genuinely have periods - sometimes hours - where I simply don't notice it at all. Other days though, it bugs the hell out of me and won't seem to quieten down. Friday 25th March, it kept me awake until 03:00, but that weekend and this past weekend, I barely notice it most of the time.