shoulder popping....?

[mike79]

For a while now my left shoulder seems to pop alot, ( no pain, doesnt pop out of joint, more so like a knuckle cracking) . Only makes the popping sound when, i do a military press/shoulder press, (arms straight up in the air, and then back down to like a front double bicep position, then it always pops right when i make the transition to straightnen my arm over my head.....any ideas what this popping could be from? any long term effects to worried about? thanks guys