newly purchased lowered 206cc knocking at the back

[blanx]

hello forum
I just purchased a 206cc which was lowered, looks nice but when driving over lumps and bumps there is a knocking from the back end, it looks like a 40 to 50mm drop (wheel is level with arch).
I've looked underneath and seen the rubbers have been removed from the arms.
Has it been lowered too much or does it need the rubbers or do i put up with the knocking.

nice forum Blanx