As Paul said, eventually it fades somewhat and you just naturally tune it out most of the time. With me, I have to stop and think about it, but when I do, it's always there.

To further what Paul said, you can get recordings of all sorts of nature-sounds. I like rain and so does my wife, so every night my computer plays rain-sounds when I'm/we're ready to crash (she's more of a night-owl and sometimes stays up late watching the tube in the front room.)