FLA1001 washer noisey on spin knocking?

I have a FLA1001w Zanussi machine that has started making quite an alarming banging/knocking when spinning 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.
I have also raised the front of the machine which made not difference.
The machine knocks but much less with no load.
Does anyone have any ideas what it could be? Could it be a loose balance weight?????

Thanks
Darren