right i've had the same problem and i tracked it down to my wishbone. i measured it all from every angle and couldn't find anything wrong untill i just put my flat metal ruler along the front seam of the wishbone to measure the height above centre for the ball joint mounting. does that make sense?
so if the wishbone goes left to right as you look at it from the front of the car, i put the ruler skinny side aginst the seam of the wishbone (where the top and bottom parts are welded together) and let the ruler overhang the end of the wishbone. i then measured the height of the end of the wishbone above the ruler.
i found that the side that had, had a knock was higher above the ruler than the good side. basicly the wishbone had bent up at the end and caused the bottom of the hub to move towards the middle of the car a bit, cos the balljoint was at a different angle. the wheel also had more positive camber compared with the other side and the whole wheel was more inside the arch.