I've had the popping sounds on back of my head & neck from starting Prozac long ago. And horrible painful brain zaps from quitting cymbalta - not on anything now except klonopin. But doesn't sound like you're saying it's med related? If there have been no med changes this sounds like when I've had a thing called a kundalini release, has to do with stuffed blocked energies along chakras & meridians finally blasting through crown head chakra. Can be quite uncomfortable at the time but worth it as it is healing enlightening balancing in result.