Haro's clicking front reminds me to ask about this clicking in my Ultegra rear. I believe it must be located in the hub and friends suggest maybe the cassett palls. I've had it apart and relubed and inspected the bearings and cassett. No change.
It clicks in cadence with the wheel rotation and stops when not rotating the pedals. I can't hear it when unweighted like on a stand. It even stopped briefly after I had it clamped on a stand a couple days. Usually it hangs by the rims on ceiling hooks for storage. It does vary if I tip the bike side to side, I think decreasing leaning left. Sound familiar to anyone?