The field sepulchra blog has a fantastic post by Rob Bridgett about recorded silences. Blurb:
Listening back to many of these recordings, it is clear they are still recordings of ‘something’, there is activity that just about be heard in nearly all of these recordings. What that barely perceptible activity is, I usually have no idea, and even though it could just be traffic, or construction, there is a human narrative element behind everything that you hear. In the same way that those historical ‘minutes of silence’ represented a very significant moment, these muted, micro sounds, bear a strange human significance beyond the recording that we will never understand.