Is my baby shoulder joint dislocated.

Every time when I lift my 6 months old baby from the crib I hear a crack at the shoulder joint. My baby is quite active and strong for his age. At times when he don't feel like sleeping he would pull his head to the back when I am carrying him and trying to put him to sleep. As I was carrying him while seated I usually hear crack too at the shoulder joint. I have checked with the doctor at the polyclinic and 2 doctors said no. My baby still uses his hands for scooting. Can anyone share their experiences?