Hey!!
I know how you feel, I had this problem for a very long time on my MK2 golf and nowone was able to help me. Replace both ball joints whiles you are at it and I promise it will go away you can say F*** Off to the hole knock, knock, knocking crap.
They shouldn't be more than ?20 to ?30 at the most and don't take long to replace.
Don't t do like me spent loads of money replaced complete driveshaft, engine mounts and it was all down to a F***** ball joint.
Good Luck
Hope it helps
Jose