I've done a lot of experimentation since my previous post, and I've found that the level of the hum in my right ear, as well as the high-frequency tinnitus in my left ear, both seem to be directly related to how blocked my ears feel, apparently due to blocked Eustachian tubes.
I have the exact same symptoms as you but on the left ear (80 Hz, varies with head position, easily masked by other low tones like fridge and ventilation). I got mine from a drone concert a bit more than two years ago; for the first few months, I was totally depressed. Now, I don't think about it as often, mostly because I keep myself busy, and there's always at least a bit of noise around me (even in my apartment, I can hear some ventilation from outside; I live in the center of a busy city). But at times like tonight, I find myself sitting in silence and hearing it blast really loud.
Reading your experiments does help a bit, especially the potential link between Eustachian tube inflammation and allergies/allergy medication...