I grew up in Reading, just outside London. My parents house was underneath the flightpath to Heathrow Airport and less than half a mile from the M4 Motorway. There is no such thing as silence there. Even in the dead of night you can hear the sound of distant juggernaughts.
Especially in the middle of a cold still night when the silence should be at its best.
After a while, you learn to block it out. You'll be happily enjoying a quiet moment, then you notice it again. You begin to pick up on the noise of different vehicles, the noise of a high powered motorbike overtaking, a police car following soon after. And always, the drone of many rolling tyres.
These days I live in London, and whilst the noises are different, they're still the same. The 24/7 westward bound commuter trains from Paddington Station. The familiar noise of cars on the Western Expressway. The underground rattling underneath. Planes overhead. More police cars. More stereos. More background noise.
Even when I'm not there, I still hear it. My mind is so used to blocking it out that it's absense creates the inverse sound. It has the same effect. But it's even more intrusive.
Sometimes I wish it wasn't this way.