Yeah this actually happened to me once, maybe four or five years back now. I was out near the coast, doing a bit of landscape photography around dusk, and I got this really intense high-pitched tone in my left ear specifically - not both, just the left. It wasn't tinnitus, I've had that before and it feels different. This was almost like a signal, very clean and steady. Then I basically lost about 40 minutes that I genuinely cannot account for.
What I find interesting from a research standpoint is that infrasound has been documented to cause some pretty strange physiological effects, including auditory phenomena, and there are certain geological features along the Pacific coast that could theoretically produce that. So I tend to lean toward a natural explanation first, but I honestly can't fully close the door on it.
Did the ringing in your case have a particular quality to it? Like a tone you could roughly place, or more of a static kind of thing? That detail might actually be useful for comparing accounts.