I've PTSD and insomnia, and trust me, whispering has the exact opposite effect on me. Whispering, admittedly, does venture partially into white noise and perhaps for some people it works, especially if you imagine it's a cute girl whispering in your ear (which explains why some of these girls on youtube get so many views).
The sound of rain, which is perhaps the best white noise delivery, especially on headphones to get the full binaural effect (stereo field), has a proven and dramatic effect on people suffering from both insomnia and/or tinnitus (ringing in the ear).
I've done sound research since 1978, mainly out of necessity, and sound has an enormous effect on our mental well being. It can be used as a weapon (loud rock music against an enemy for example), or can be used to cure numerous ailments. Music, for example, can be and has been life-saving. If I didn't have music, I would have been in the grave long ago.
What is white noise?
In simple terms, white noise is a special type of sound signal which is used to mask background sounds. When used to promote healthy sleep, white noise helps to drown out sounds which might otherwise prevent you from either falling asleep or waking up whilst asleep.
For more on white noise and it's effects on sleep, check out this link: http://sleepjunkies.com/features/sleep-soundly-with-white-noise/
Anyhizzle, check out this rain track, recorded in full binaural stereo...if you get sleepy, you can thank me later when you wake up. In the meantime, I'm gonna listen and then zzzzzzzzzzzz.