I had this on mine Dunk! Over uneven ground and slight bumps i got a knocking.. I was told it was my top mounts etc and took it somewhere else to have it MOT'd and it turned out that one of the droplinks had about 2/3mm play in it. Had it changed and its gone away!!
All was well and they were fitted this morning - you really get used to how unstable the car is with worn shocks. It feels crisp and tight and stable as anything now ... and knock free too