Just inside each strut tower (the towers each have 3 silver bolts/nuts) there is a brace/bracket between the two towers (black horizontal bar in picture below). Each end of this bracket has 2 black bolts/screws that hold it in place and these are what need to be tightened. 12mm IIRC.
I have a similar clunking noise from my front shocks.
Could you please re-attach the pics. They are not available here.