What Causes Fluttering Feeling Between The Knees And Shin?

I have a fluttering/vibrating sensation in my left leg. Primarily it s right below my knee to the outside edge and travels down the outer edge of the shin some. I ve also noticed it along the outside of my left thigh. It doesn t hurt, but it s very distracting and annoying. I don t smoke nor drink much caffeine and I m under minimal stress. What could be causing this?