Knee popping when i extend my leg?

Sometimes when i extend my leg, i'll get this like weird feeling in my knee and as soon as i bend my knee it pops. Slight pain when it pops but nothing afterwards. I can bend it and walk/run w/o pain. The other day i was walking then i felt the feeling like it was on the brink of popping. It made the walking difficult until i popped it by bending my knee. A little difficulty for a step or two then i was back to normal. Any help would be nice besides go to a doctor. (Not saying i don't wanna go but i'd like to see if anyone has similar issues)