So anyway, some thoughts by Ajahn Sumedho and John Cage (whom I believe was a Zen practitioner) on the 'sound of silence':
How does what you call the “sound of silence” relate to “relaxed attention?”
I have found in my own practice when I am in this relaxed attention state, and I’m not absorbed or focused on anything in particular, that I hear this kind of high-pitched vibration or a sound of whatever it seems to be. I call it the “sound of silence.” It’s kind of like the background of everything. And so once that’s recognized, then I find that it is like a stream that you can rest in, and it allows both attention on this wide spectrum of awareness and it stops the thinking mind.
The “sound of silence” can serve as a point of reference, to know when you’re in the natural state of awareness. It means having a relaxed attention towards the feelings in your own body, your emotional states, and your thoughts and memories. You are experiencing them from the perspective of this empty place rather than the endless reactivity that the mind usually has to your feelings or emotions. It’s not a created sign, something that you have to perpetuate. It’s just a matter of recognizing and trusting in your relationship to the world around you.
The encouragement is to recognize and learn how to rest in relaxed attention rather than trying to concentrate the mind or get in a particular state you imagine you should have. Your relationship to the conditioned world becomes one of awareness and reflecting on the nature of impermanence.
The sound of silence is not an object that you have to sustain through concentrating upon it, it’s just recognizing and trusting it so that whether you are aware of it or not, it’s still there.
Cage: 'If you develop an ear for sounds that are musical it is like developing an ego. You begin to refuse sounds that are not musical and that way cut yourself off from a good deal of experience.'