Today after warming up with some stretching and glute activation work I started to do some power cleans. On my first rep I got a "tightness" (best way I can describe the feeling) in my left glute a little bit above where the hamstring ties in to it. This has happened in the past as well when doing power snatches (in the left and right glute, but its always only on one side when it happens). Stretching did not seem to alleviate the problem at all. Any feed back as to what might cause this and how to avoid it in the future would be greatly appreciated.
Try foam rolling the area with a LAX ball.
Stretch out your quads, it could be a tightness in your quads tilting your hips forwards.