Steering knocking sound

[Jimmy_GTT]

When I turne the steering wheel to the left or to the right (just a little bit) and than turn it to the opposite way I have a knocking sound. What could it be?
Thanks!

[Jimmy_GTT]

Does anyone knows how to adjust the 'dumper adjusting nut' of the steering rack?
Could it be adjusted if the rack is in the car?
I can hear the knocking noise from the center of the steering gear. But I do not know if adjusting this nut could make any difference.
Thanks