Namaste to all. Thank you very much for sharing your experiences regarding the Divine Sound. It has inspired me to return the favour by sharing my own experience, in the hope that others may benefit--as I have benefited from the generosity of others.
My experience appears to be similar to Lila's. The Sound has been with me for many years, and I believe it started shortly after being initiated into Kriya Yoga. It is a wondrous sound. It appears to be omnipresent, coming from no particular direction. It is ineffable--almost impossible to describe. The best approximation I can come up with is like the beeping of a telegraph but very high pitched and with an extremely short interval between beeps, with a bell-like sonorous ringing quality suffused throughout. It is in the background--I can often hear it clearly at night, and sometimes during the day if I am in silence or concentrate. The quality of the sound changes slightly depending on my physical and mental condition and lifestyle. At times when I have gotten out of the meditation routine or have been in a state of dis-ease, it has appeared to temporarily depart, sometimes for as long as several months--but it always came back. It has never disturbed; in fact, it is very soothing. It does not bother me and I do not bother it. I just let it do what is has to do and am truly grateful for the blessing.
I've grown up with a lot of New Age nonsense, so have developed what I believe is a healthy skepticism. Thus, I've experimented with the sound and tried to rule out medical tinnitus (but did not have it medically checked as it never bothered me). I tried closing both ears, one by one. It is not coming from one side. It does appear to be coming from somewhere deep within. If I close both ears very tightly, the sound becomes somewhat muffled. Although I can hear it without physically closing my ears, the most clear and resonant sound comes when I close both ears very slightly.
On a side note, my senses of hearing and smell have always been my most acute senses (perhaps as a consequence of my weak eyesight). In addition to the Divine Hearing, I have also had extra-sensory experiences of smell (for instance, smelling things over the telephone). It seems to be that the Sound and the Smell might be related, as they are in biology.
I don't have many "experiences" but this is something that has been with me for some time and I hope it is helpful for people. I am blessed to be around people who distinctly and clearly hear all of the Divine internal sounds at will, so I am just happy and filled with gratitude that the Divine seems to be starting its work on me... !
Thank you all again.
Tat Tvam Asi