Started biking about 5 months ago. Everything was going fine (riding up-to 3 hours comfortably) and then started having discomfort in left knee. Sensations vary, sometimes it feels like burning in the area of the petella and other times some low-grade pain in the actual knee joint itself (more prominent on medial side). At times the right knee flares-up as well. In any case, I'm concerned that if I continue to ride, permanent damage may result. I have adjusted the seatpost as high as it can go without my hips rocking when pedaling. I have noticed that a plumb line intersecting the middle of the pedal also intersects the middle of the knee joint as opposed to just in front of the knee cap. No fore/aft adjustment of the seat will remedy this. I ride with regular pedals and regular shoes at this time (no clipless pedals or cages). I know the best answer is to have a professional evaluate my set-up, but I hope to fix this situation without the expense if at all possible. Any suggestions greatly appreciated.