Runner's knee

Since the 13.1 on May 1st I have been running 6 miles on the weekend (long and slow) and 3 or 4 miles during the week- long and slow with some short, fast intervals. On the 6 mile runs I have been getting a pain in the knee, short runs were OK. Today I started getting the pain on my 6 mile run so I tried running faster and it went away? I think when I use the Chi Running method (which is a faster pace for me), I have a different stride and that must be why the pain in my knee goes away. Any who, I am going to try running faster next week on my short runs and see what happens.