I'd never heard of this hum thing–but it makes sense.

When I attempted to enlist in the early 90s, I discovered that I have very interesting hearing. During the physical, they do an elaborate hearing test. I didn't know this–and, because of what they did, I got worried.

They did the test on everyone and sent them on to the next stop in the physical, but they kept me back and had me keep doing the test–I think they kept me in the 'tank' for a good half hour–I was afraid that there was something wrong with my hearing.

When they were done they explained that they'd taken the sound up and down, beyond the normal range because I appear to have hearing that extended a bit outside that range–something they'd seen before, but that was unusual.

And they explained a lot of things–including that I didn't have tinnitus. That the constant noise I hear is actually there, that it's high and low frequency sounds that are a simple by-product of modern liife.

Perhaps thats the source of the 'hum'–people with a slighly bigger hearing range.

I wanted to reply to your post for the simple reason that i experiences the same thing last night.  I had gone to bed and was woke up by what at first i thought was a television up stairs. But my mom had gone to bed and was silent. Then i realized it sounded like lots of people talking in a tunnel that i couldnt make out. It was a very disturbing experience. I have lived here foe over ten years and never heard or saw anything. Numerous other people have though.

dammit.  i wrote a post and then it told me that my math was incorrect!  surely, at age 33, i know how to do simple math?  i mean, i rock at calculus; why can't i add 10+5?

anyhow, what i wrote was that i find this thread interesting from a medical standpoint.  i have a heart condition which can result in sudden cardiac arrest due to ventricular fibrillation, and in the last 5 or 6 years i have had several episodes of collapse caused by my heart going haywire and my brain failing to receive enough blood and oxygen. the episodes last several minutes, during which i am usually having what looks like a "seizure" (though I am completely out and have no clue what's going on) and each time, as i recover, i hear these sounds: a rushing, chattering, babbling cacophony of unintelligible voices as if in a tunnel.  i have always chalked it up to the re-establishment of proper brain function: neurons firing, neurotransmitters being released, blood pressure being equalized, etc.  the sounds are so "loud" that they prohibit me from being able to hear anything else (such as the people panicking around me), but they are very clearly originating inside my own head. 

so, besides the obvious mental illnesses, such as psychosis (which can sometimes be limited and short-term), schizophrenia, bipolar, etc., i believe it is possible that this phenomenon could sometimes originate as a result of oxygen or blood-pressure problems.  is anyone experiencing any other physical discomforts like fatigue, dizziness, etc? it seems like most of us on this thread are actually skeptics, and aren't willing to immediately dismiss it as paranormal, so it might be important to get a medical opinion, even if it is scary to march into your doctor's office and say, "hey, i'm hearing voices!"

anyhow, i am also on betablockers for my heart condition, so i feal ya, learjet.  metoprolol has sapped my heathy creativity, and left exhaustion and depression in its wake.  here's hoping we can find a happy middle ground between our illnesses and our emotional needs.