Yeah actually this is interesting because I've spoken to a few people locally who've described something similar and the humming detail keeps coming up unprompted. Like they don't even realise it's significant until you point it out.
My mate had a missing time episode out on the moors about two years back and he said the first thing he noticed was this low resonant hum he could almost feel more than hear. Lasted maybe 30 seconds before he lost about 90 minutes.
What gets me is whether the humming is the cause or just a side effect of whatever's happening. Could be something to do with infrasound affecting perception and memory, there's actually some decent research on infrasound triggering disorientation and even hallucinations. But that still doesn't explain the time loss part.
Has anyone done any EVP recording during or after one of these episodes? I'm genuinely curious whether anything gets picked up in that frequency range. Would love to compare notes with people who have documented theirs properly rather than just going off memory.