What is this curious noise ?

Ezy Rider
Ezy Rider Posts: 415
edited January 2012 in Workshop
When Im on my roadbike on flats or climbs and i have to get out of the saddle and sway the bike from side to side as you do, I get this clanking sound while i pedal that isnt there when Im sitting and pedalling. Ive tightened any allen bolts at the crank and seatpost, but yet it persists. One thing I noticed is that some of the spokes on my rear wheel have lost some tension and stiffness and im thinking of taking it to lbs to have them re-tensioned, wheel is running true though.Im puzzled as to what could be causing the noise which occurs during the pedalling and swaying motion only..................any thoughts ?