There's no such thing as silence (if you're not deaf). You can always hear your own heartbeat and respiration. Silence is also a very subjective experience. We can hear (or imagine) inner sounds when watching or smelling something particular (synergy). I can play whole songs in my head while walking without the aid of a an MP3. People can go crazy if they have to stay in accoustic "dead" rooms (like sound studio's, deprivation chambers, underground mines, spaceships) because lack of sound is very freightehing, like a non-presence. In music, most common in postrock, loud can only be loud if there is also silence to contrast it. When I wan to go someplace silent, I wait for a snowfall. Snow is a great sound absorber. In a snowy mountain forest the heavy leaves won't rustle, so you hardly hear any wind sounds. Colder and thinner air will also give sound less volume.