Check if any of the concrete weights have come loose?
Possibly a problem with the damping system - shock absorbers at the bottom of the drum which are meant to minimize oscillations. They're two main types, either sliding pistons or a sprung friction pads which bear onto friction plates welded to the drum. Whichever type they are, they're probably worn out and needing replaced. They suppress the oscillations of the drum when in spin mode so the machine doesnt hop around the floor. Friction dampers are like little square brake pads attached to sprung arms mounted on the machine frame which bear onto friction plates attached to the drum. Any excess movement of the drum is dissipated by friction between the two surfaces. If they are the friction type, prise the sprung arms apart with a length of wood, and replace the pads. The other type is a sliding damper, which is like a scaled down version of a shock absorber in a car.
If there is a rattling sound when you move the drum backwards and forwards it could possibly be that one of the top springs have snapped. This would cause the pulley to rub on the back of the cabinet when washing, which would then make a scraping noise as well. Replacement springs are available from spares stockists.
Repair and service your own washing machine. Go to www.2ndwave.co.uk/manual.html
dannyboy, November 2008