Whenever I am doing my pre workout stretch, I have noticed both my shoulders popping. (see image below)Particulary when I put my arms behind my back and lift up. Anybody have an idea what could be causing this? It doesn't hurt or anything, it's just strange how they pop every time I do it.

http://www.juniorbaseball.com/skillsclinics/morearticles/images/frontshoulder_stretch.jpg

Jason

I'll jump in on this one. I think popping noises usually come from a tendon or ligament snapping across the bone. Particularly if it always happens in the same position of the stretching movement it tells you that a particular ligament or tendon is jumping from one groove to another. I don't think there's anything inherently bad about this. However, I could see that if you did it repeatedly and forcefully it could put some extra stress on it and maybe cause some inflamation (tendonitis).
If you warm up your shoulders first and stretch them more slowly, maybe the tissue would be a little more loose and sort of slide rather than snap. Just a theory but in the long run the extra care might result in better joint mobility and a decreased risk of connective tissue injury.
That said I wouldn't worry about it too much. I love doing lateral raises all the way up (over my head) and my shoulders make noise every time. But it's never bothered me.