I actually just finished reading Kelly Starrett’s book and have began trying some of the banded distraction techniques (both for my hips and shoulders). The fact that mine goes away when I’m warm makes me wonder if it might also be a hip flexor thing too. I actually get more discomfort in the front of my hip doing box jumps than squats, squats usually bother the back of my butt/leg more but I also know that impingement can refer pain to unsuspected places.