White noise + earplugs Question: when it actually is very quiet (like 3am), does anyone else hear a low-pitched hum? It's so low and quiet, it's more like a pr

White noise + earplugs Question: when it actually is very quiet (like 3am), does anyone else hear a low-pitched hum? It's so low and quiet, it's more like a pressure than a sound. And if there's any sound at all (e.g. even if I'm moving around), I can't hear it. I'd thought it was traffic or road construction etc, but I also heard it in a forest, about 10km from the nearest main road... But it doesn't seem to be internal, as it's not synchronized with my pulse or breath. EDIT: I'm in Melbourne, Australia. I first noticed it when living by the bay near the international shipping dock, and it seemed to be coming from there. But I've just moved about 20km further along the bay, and it's just as loud. And also heard it about 100km inland (in the bush). Though this was near major high-tension powerlines (I think, supplying melbourne with coal-electricity from Morwell). Maybe that was it.