Today when i was on my MTb i found it felt funny. When turning the crank and pedal, it is not smooth. When i am in my lower gears i feel this sharp resistance when i pedal. It makes a small tinking noise. It is not consistant but it seems that it is one one part of the stoke. Once the in a higher gear i see that feels like the stroke is smoother. WHAT IS GOING ON??? Is it possible that this is only chain slip? I'm sorry if this is a bad discription. Not to sure how to discribe it. Thank you for you help.