sorry to come in late into this rather colourful thread, but i didn't see until just now
max, if you are still suffering from this "noise", i strongly suggest you see a qualified medical practitioner, and not try to diagnose it over the internet (or by a chiropractor or osteopath, neither of whom has anything to do with hearing)
"I noticed that by plugging my ear with a finger, the oscillation subsides, which makes me believe it is the eardrum itself which is shaking.."
the opposite would be true
if the eardrum was causing the noise, it would intensify when outside noises are blocked out
imo, the most LIKELY cause of your symptom, from the limited history you gave, is something to do with your sinuses, which can certainly be afeectd by the change in pressure inside the ear canal
however, it could also be that you are experiencing auditory hallucinations as a result of acid flashbacks....
as i said, if pain persists, see your doctor!
tomas is on the money, imo, regarding the grey matter being more important than the mechanics when it comes to sound interpretation, and, therefore, hearing