Out of balance drum on fast spin?

I have a FLA1001w Zanussi machine that has started making quite an alarming banging/knocking when spining at high speed or reving up.
I have removed the back replaced the belt and also remove the dampers which seem fine (both dampers have resistance).
The drum does not seem to have any play in the bearings from the rear or inside the drum and is quiet when turnt over manually.
Does anyone have any ideas what it could be??????

Thanks
Darren