corsa b 95 1.2 adjustable coilovers making cracking noise?

I have fitted adjustable coilovers to the front of my corsa b but when i hit ant bumps in the road there is a loud banging / cracking noise like metal to metal . I have rechecked they are fitted correctly and the top mounts are good but i can not work out how its making such a loud noise any ideas
thanks

matthew