Running knee pain

I was scheduled to run 13 miles yesterday. The day before I did an hour of aikido class. Then I cam home and ran 8 miles at pace (10:16). Then I road my mountain bike 11 hilly windy miles. I felt fine. Except it was really cold and wet on the bike ride. But yesterday when I started run on the treadmill, within a minute, I started to get a pain on side of knee (outside of left knee). When I stopped running, the pain would go away. I got back on the treadmill, and tried different speeds from quick walking speed to fast running speed, and I would get the pain in my knee. I got less than a mile of running in.
When I wasn’t running on the treadmill, my knee felt fine. No knee pain walking. I even went to karate class night, and had no problems. I took some ibuprofen hoping to eliminate any inflamation that I might have in there. I decided to skip my 13 mile run for the day. I have aikido class tonight. And my next scheduled run isn’t until Tuesday. I will try running tomorrow night and see how the knee does. Hopefully there will be no knee pain. The run is supposed to be an easy 5 miles.