I've been dealing with severe stiffness in both my quads for some time now. It's gotten to the point where I cannot squat, and I avoid going up stairs.
I'm an athlete who squats explosively, does sprints (100s,200s,400s meters). I was told that it is probably ilio-tibial band syndrome. It seems likely that it is, but I have no pain near the lateral portion of my knee at all, although I've had my knee pop once while stretching-like it came out of joint, and it stayed sore for months. I also experience a cracking and popping in the outer, center portion of my quad when going up stairs, or when extending my leg.