Hi Ping Pong Boy, sounds just like the problems I had when I first started running. Mine was caused by imbalance and an old hip injury which had left some grissly tissue. A trip to the Physio, coupled with the exercises she gave me, sorted me out immediately and I have not had the problem since.
I wholeheartedly recommend seeing a Physio as mine was extremely helpful, asked loads of questions and found the problem straight away. Good luck.