Popping Noise When chicks cheep

[waddles99]

When my chicks are cheeping, there is a faint, yet very noticeable popping/cracking noise in their chest. I have no idea what it could be. My other chicks had this then they outgrew it. What could this be? Any suggestions?

 

[sunflour]

Sorry I can't give you an answer but interested in seeing the opines here.