"Abstract Sound is called Saut-i Sarmad; all space is filled with it. The vibrations of this Sound are too fine to be either audible or visible to the material ears or eyes, since it is even difficult for the eyes to see the form and color of he ethereal vibrations on the external plane. It was the Saut-i Sarmad, the Sound of the abstract plane, which Muhammad heard in the cave of Ghar-i Hira when he became lost in his divine ideal. The Quran refers to this Sound in the words, 'Be! and all became.' Moses heard this very Sound on Mount Sinai, when in communion with God; and the same Word was audible to Christ when absorbed in his Heavenly Father in the wilderness. Shiva heard the same Anahad Nada during his Samadhi in the cave of the Himalayas. The flute of Krishna is symbolic of the same Sound. This Sound is the source of all revelation to the Masters, to whom it is revealed from within; it is because of this that they know and teach one and the same Truth." -- Hazrat Inayat Khan, The Mysticism of Sound
Hazrat Khan: "It sounds like Thunder, the roaring of the Sea, the jingling of Bells, running the Water, the Buzzing of bees, the Twittering of sparrows, the Vina, the Whistle, or the sound of Shankha..."(The Mysticism of Sound)
"The person, who is in tune with the universe, becomes like a radio receiver through which the Voice of the universe is transmitted." (Hazrat Khan)