Popping isn't too much of an issue but grinding and crunching and any associated pain obviously is. I think you might be looking at the symptom rather than the cause by just considering the knees. I can't quite understand what you mean when you say "underpronate" because that would typically not result in the "knees in" position you refer to. Whatever the case, I think you might want to look to your feet before you look to your knees. It sounds like it may be the cause rather than the effect of your problems. It often helps to fix things from the ground up. Sometimes, this can be done simply by balancing the foot and ankle musculature. In extreme cases, orthotic intervention may be necessary. Can you tell us a little more about your feet? Like where are they at foot strike and toe off, what parts of the shoe do you wear out first, etc.