The sound of silence

No not the song by Simon and Garfunkel written in the aftermath of the Kennedy assasination.
I am talking about that sound that exists when all other sound is removed. Not everyone hears it or so they say, I think everyone has the ability to hear it but we have very few times in our lives where we can enjoy total silence. The sound is like a resonating hum. It is constant and deafening when all other sound is gone. I actually cannot stand to hear it for long because it is so loud to me that it is hard to deal with.. so I usually find a way to create sound so that I no longer hear it. White noise as I have previously stated is an old friend of mine and it helps cover up that sound as well.
Still I wonder what this sound is. Is it the sound of the earth itself?