Is it like right in the back of your neck? It can be fluid from the spine moving around. I have that sometimes.
The sound is most likely related to degeneration of the discs of the cervical spine, possibly arthritis. On the research I did one lady said she used a product called "Angelica" and it stopped her problem. She also had dizziness as well and it stopped it too.
Please check with your doctor on your condition and ask about Angelica. You might want to research the med before going to the doctor so you can tell him what's in it etc. because it is not a prescription medicine your doc may not be familiar with it.
I hope this helps. Have A Nice Day!
Could it be your jaws when chewing? I know mine make a grinding popping sound occasional.