Help- Clanking/Knocking Noise

twotyred
twotyred Posts: 822
edited July 2010 in Workshop
When I stand up to pedal I'm getting a clanking/knocking sound from the area of the bottom bracket which happens once every pedal stroke. No noise when I'm seated to matter how hard I pedal.

The chainset and bottom bracket are Shimano 105. I've disassembled the chainset from the bottom bracket and checked the BB bearings are screwed firmly to the frame. The bearings are running smoothly and there's no apparent movement. I've made sure the bolts fixing the chainrings to the spider are tight and have re-fitted the chainset making sure the pinch bolts are torqued down properly. The pedals are firmly screwed into the crank arms.

None of the above has made any difference. Any suggestions please?