It could be a number of things, it's kind of hard to say.
I doubt it's your binding angle, usually you will get knee pain if it's related to binding angles or width as your knees will experience the most pressure from an unnatural stance.
Is it both legs or just one? Have you had any issues in the past with your legs? Does it hurt if you go running?
I'm thinking, since you mentioned plowing down the mountain, it could be from excessive heel side. When you pull your toes up toward your shins, the front of your shins flex. It's odd that you would get pain from it though.