Ford Focus -drivers side window -making clucking noise - up or down?

I have a Y reg Ford Focus- Some other posts have similar problems with the driver's side window, operated by a motor. Mine still works, but makes a cuck noise at certain stages of the movement- either going up or dowm. It got stuck the other day. I managed to free it and it is still making the clucking sound. I have stripped the door and sprayed WD40 but I can't fathom what the fault is !