Sounds bizarre but i keep hearing a crunching sound at back of my head when i walk, just wondering why?

Osteoarthritis: Popping sounds can sometimes heard when muscle or tendon slides over a bony bump. Joint changes such as traumatic, degenerative (osteoarthritis), and inflammation as you turn your neck often produce noises. A courser grinding or crunching may indicate more advanced changes in the surfaces of one or more joints. If pain associated with noise physical therapy and anti-inflammatory agents can help.