It's hard to say what it could be because the sounds you describe could be normal. Necks and joints do pop from time to time. It could be something, it could be nothing. Not to scare you, but please get it checked out. I've had a lot of popping/clicking in my joint since I was a teenager (I used to purposely gross people out with these sounds for my own amusement) and five years ago new grinding sounds started at the base of my neck. This has led into a lot of physical issues and now I must go to a specialist. Make a visit to the Dr. and before you go make note of any issues you may have with range of motion, headaches, nausea, dizziness or stiffness. Blood tests are useful in these cases because they can detect inflammation and possible joint disease. Better to get it check out and be safe.