I have this too at bad satanic levels. The worst is hearing it in music, rivers/waves, or when speaking.
Ironically it started with exposure to steroids... namely coming "off" of them during the taper.
It exploded during HBO therapy. My guess is oxidative stress and a form of reactive tinnitus you normally can't hear... either nerve death or nerve myelin damage (option 2 is the hopeful one).
White noise really brings it out. I had a period where it got better slightly but my GP recommended another course of steroids if it was "that bad" which made me conclude (after waking up to full blown ear fullness like a concert happened) on tapering that steroids caused it.
Theory is re-bound immune reaction from suppression and too fast taper off Prednisone, causing lesions like MS... so long as nerves aren't dying that myelin can be repaired. It would limit the nerves "insulation" likely resulting in induced firing from other nerves closeby (sound familiar to this distortion BS?)
Ironically I'd never have known because like benzos, it only happens "after".
It did... slowly... improve... once... weeks ago... but I think that was due to slow sound exposures and being gentle (as in it took greater volumes to provoke its appearance).
Benzos targeting A5 GABA subunits (Clonazepam, Zopiclone) 100% make it go away... Melatonin seems to help as well as alcohol (a bit but tonal tinnitus comes out a lot) and coffee both help... so maybe there's a mechanism that needs time to upregulate the receptors naturally. Prednisone helps initially but leaves parting gifts and makes it worse overall. DXM helped but caused other strange effects so I wouldn't suggest. Memantine has too long a half life for me to know if it helped.
CBD seems to make it worse... but nailbiting tonal tinnitus went down.
A potassium channel modulator would likely work if it existed... given it's akin to kindling and a seizure.
Anyone tried Gabapentin on this? It'd be a lot safer than benzos.
This is probably one of those things where time and promoting nerve health/growth through diet and activities whatever way you can might be the way to go, and therefore if it works it'd be slow anyways like any brain injury to get over, when I was getting better I limited noise a lot, used vitamins, Melatonin, tried light exercise (that makes it worse when I lift weights) and limited sound exposure to 50 dB, used a lot of fast music to mask it (might help retrain the nerves?). Those all likely "helped"... along with "normal" inflammation.
Before it got worse from steroids, it "was" getting better, I could tell listening to things that it kindled still but sounded "quieter". It even got to the point in mornings I could take out earplugs and I'd get a good 30 seconds to a minute before the orchestra ramped up.