Whenever I pedal, regardless of the gear, I feel a sensation in my soles like I'm turning one of those manual coffee grinders. I can't hear a distinct sound, though.
Turning the pedals backwards, the movement is smooth except for a specific part (left pedal between 5 and 6 o'clock) when it also makes a weird sound.
What could be happening down there? (I'm reluctant to start servicing it)