I also had a cracking or crunching sound while turning or moving my head. I had a habit of cracking my neck due to increasing stiffness. Turns out the crunching sound was my vertebrae in my neck due to disk narrowing. I would recommend going to your dr for a ct or mri to see whether you have disk issues.
The cracking noise in your neck is just that, your neck joints are cracking just like when people crack their fingers. My son does this but he really has to exaggerate his head movement to do it. So you may be doing this same thing just to see if the crack will happen again. The advise of experts is that neck cracking can cause problems down the road. So if you can help it, don't do that anymore.
As far as "something moving around my head" you would need to elaborate more on that.