What is causing my neck to pop??

[bubblygum]

Every now and then, the upper part of my spine, the back of my neck, kind of locks for a second, and then pops back.
If you place your hand there when it happens you can feel it moving.

I was diagnosed with scoliosis a couple of months back and i dont know if it is related or not.

It doesnt happen all of the time, but when it does it is very uncomfortable. Sometimes painful.

Has anybody experienced anything like this? What was the cause?