It is said that the sound of silence is more deafening than any other audible sound...why is that so?

We are so used to hearing sound (even our own heartbeats) that the absence of sound becomes a huge shocker. EVen standing up in an isolated recording studio 'sounds' weird for first timers. In a recording studio, it isnt PERFECTLY silent, but can be quiet enough to make the point. Silence is unusual. Being in a silent environment feels almost 'unhealthy'.