Does this happen when you change gears from 1st into 2nd? If so then you need a new transmission mount, they only cost about â¬50 and you can fit it yourself if you can, or get it fitted for about â¬40, thats what it cost me, and it's made a huge difference, the sloppy gear change, and weird knocking has gone, this seems to be quite common and quite an easy fix.
More than likely it wont be your engine mounts, unless your car has been used for rallying.
Hope this helps!