When I roll my head around my neck, I hear a soft, crunching noise. Does anyone know what causes this sound?

I feel it is my duty to comment on this question, because my fluther name sounds a little like that soft crunching noise. The Occiput is the bone in your skull that is in the back where your skull meets your neck. Directly below it in your spine is the first vertebral bone, the Atlas. You'll notice the crunching noise mostly occurs when you extend your head back. That's because there's no cartilage in that area. What you're hearing is the sound of the two bones rubbing together--a sound that happens all over your body, but only in this one joint do you hear it, because your occiput is also connected to the bones that mediate sound in your head--the malleus incus and stapes. They vibrate along with the slight vibration communicated from the spot between your atlas and your occipital bone, they vibrate too, and you hear a soft crunch. So I don't know about any injuries caused by tipping your head back, but I wouldn't do it all the time--there's no padding back there.