The machine is now fixed!! I got a man in he completely dismantled the machine to show that the problem was with the aluminium Y shaped spreader that fits over the main shaft and extends to the outer rim of the stainless steel drum. Two of the three arms had corroded through completely and sa a consequense the drum was jumping about like a wild thing. He used an angle grinder to remove the drum then replaced the main shaft and aluminium spreader - bolting itin place. It is now woderfully quiet. Total time taken 4 hours.
Alec Gurney., February 2011