pain on the inside of the knees when biking uphill

hi, i just did triple bypass colorado ride (120 miles, 3 mountain passes, over 10,000ft elevation gain) last weekend and after about 50 miles i started feeling pain on the inside of my knees, i only felt this once before when i did another century ride in buena vista, colorado in the spring, there were a lot of uphill there too, I mostly feel the pain when I ride uphill, it feels like joint pain, not bad enough to quit, but consistent, i felt it the whole day after the ride as well, on my training rides i don't normally do sustained steep hills, and never (even on long rides) experience knee pain. my friend told me this could be caused by my seat being too high, but i don't feel uncomfortable when i ride. does anybody have the same problem? or knows why could this be. any input would be appriciated, thanks