Hi unfortunately this whole range of dryers have been plagued by drum and bearing issues. Its likely the cause will be a problem with the drum shaft. Remove the rear bearing guard the light grey platic cover on the rear, and check for any damage or worn components. If all seems ok its possible one of the fans have come adrift from the motor or the belt tension pulley is broken. To check these remove the lid and the left hand panel ( looking from rear )
looking down following the belt you'll find the small plastic pulley check its not split and the centre brass bush hasn't worn away.If thats ok lever up the fan cover its the dome shaped cover at the front and check the fans for damage/wear.I know its a lot to check but its one of those faults with many possible causes.
Jim
February 2012