The soft noise I continually hear inside my head when I listen for it, or when it is really quiet, or late, or I'm really sick, even if I don't try to listen for it.

The sound is most basically a soft, harsh, high-pitched tone. But it is not perfectly static. It has a soft of subtle vibrato. There are all kinds of overtones and under-pitches to it. The volume varies, depending on a number of environmental factors, health, stress, etc. I can tell when I am getting sick by the quality of this sound.

I like to think that I am hearing the impulses of a trillion neurons, a sort of pulse or the background noise of my brain.

The noise of insanity? Probably it sounds different to everyone... For me, it's the directionless sound of waves hitting the shore of a large body of water. Large waves, the type kicked up by a strong wind or a storm on the horizon. Raw power, uncontrolled and threatening to destroy all you hold dear, but still a force of nature with no controlling will.

The noise is only one component. Consider also the premonition that the tsunami is behind, about to come crashing down. A vision of destruction, that this huge mass of water will carry you away never to exist again. A chill, an odor, a feeling of impending loss of control and doom.

Although profoundly disturbing, i wouldn't trade the ability to experience this for any Prozac, Soma, or psychochemical peace of mind.