Pressure.
Vascular- My T sounded like a bird chirping for 1.5 years, in my right ear only. The whole time I had high blood pressure and pulsatile T in both ears. I finally got sleeping again with medications and a hearing aid that masks the bird noise. Pulsatile T of coarse gone, but being able to relax and sleep and masking the bird noise has reduced the Bird Noise dramatically, I believe high blood pressure in the ear was the problem.
Hormonal - Oxytocin Nasal Sprays have been reported to help reduce T, this may be marketing but it seems to make sense given the properties of oxytocin that it could help. I found some on Amazon so who knows but I bought two brands. I will update you if I notice any benefit. I've noticed there is a connection between the Nasal Passage and Hearing/Tinnitus, I think they are Innvervated together. When I had high blood pressure I also was breathing really heavily through my nose and it was "wheezing" and I shit you not the "wheezing" sounded identical to the "Bird Noise" and when I finaly started sleeping again and stopped wheezing through my nose the bird noise T also has almost completely gone away.
Off- Topic but... Good information is good information.
Cochlear - Cochlear Hydrops (increased pressure inside the inner ear (cause unknown)), this pressure causes "fluctuating" tinnitus as the pressure within the Cochlea fluctuates. You wont know if you have hydrops unless you get tested by an otologist, or if you unfortunately develop menieres. Its possible you have Cochlear Hydrops in your hearing chamber. The symptoms are fluctuating hearing loss and Tinnitus as well as vertigo (in most cases but not all) most people with hydrops like me never have such severe pressure that the chamber ruptures causing vertigo and so they never develope full menieres, but they have the precursor called Hydrops and they experience hearing loss and Tinnitus and don't know why. Good news is that you can stop the Hydrops, but they don't know how, probably through diet and exercise. A video on hydrops