Hey freefall,

I think I know what you mean and I have posted about this some time ago myself. One responce I got was it was the actuall sound of your blood running through your veins near your ear cannal.

I guess this makes sense. The person said it was more apparent in people with high-blood pressure. Even though I don't have high blood pressure, I believe it's a possibility.

I also concur with Deja's "tone replacemet" explanation as well. Many people listen to music or watch tv before bed, and may not realize how loud it is untill they finally "hear the silence "of bedtime.