Mine started c 1979 when shooting pistol competitively and TREing on the Bandit. Sheesh, that's a noisy machine. I then had an ear infection which made it difficult to lie on either ear. A dull pressure ache.
I was prescribed Terramycin. Bad, bad choice it seems. Look up links with tinnitus.
A later problem - and seemingly an American professor, Fatima Husain, has linked the problem with racing minds. It's certainly true in my case. Sadly I'm too old for her studies but was greatly interested.
Ringing in Ears Keeps Brain More at Attention and Less at Rest - Neuroscience News
In haste