Turn it off at the mains. If it is under a counter, pull it out so that you can take the lid off it. The drum is suspended in place by a collection of springs, struts and dampers and there are usually a couple of hefty concrete blocks as well. Have a look inside for one of the following - Concrete weights loose or breaking apart/fallen off. Suspension struts no longer securely attached to the drum and casing. Springs broken or detached. Good luck
Richard, December 2008