Shoulder blade cracking

I have notice my boyfriend when he rubs my back my right shoulder blade pops but it happend when my boyfriend rubs that same area over and over. since my upper back area so stiff its hard for me to stand still so he has to hold me down and it like pops but my shoulder moves too. i don't know if its normal or what. does it happen to anyone ? & right now i haven't done it in forever & it starting to hurt there. I'm not   pregnant or anything just to let you know because i looked up a topic question and it was a pregnant woman. It makes me so curious to know what is this Technque