Autonomous sensory meridian response, if real, might just be the pleasure centre of the brain reacting to a feeling of intimacy generated by whispering, plus the blessed relief that comes with finally getting some peace and quiet from the noisy world for once. The white noise represents that quiet nicely and, as a bonus, comes with the high-gain settings necessary to capture whispering on a microphone.
Mokalus of Borg
PS - I'm not completely convinced.
PPS - I haven't had it myself, anyway.