For any "strange" feeling, even if it's not pain, talk to your doctor. You may not need to cut back or stop, or maybe you should. Your doc can examine you, maybe even do some imaging of your knees, and then go from there. It may also benefit you (after seeing your doc) to seek out a local physical therapist who can do a gait analysis on you, to see if the way you run is causing your strange feeling. A good sports PT can also guide you into making changes to lessen your chances of injury in the future.