got a knocking on my corsa activ 2004 model?

when i steer right i have a knocking noise under my feet.changed drive shaft,brakes,wishbone,trac rod end and down rod link also wheel bearing.when clutch pressed in the knocking goes of course the car is still moving.been told it mite be gear box.at my wiittsend with it as any body had this problem before or as as any idea what it is
many thanks for any help