Is there any side to side play in the inner bowl? If so then either bearings have failed (it will also be noisy on fast spin) or bowl securing clamp has loosened. If no side play in bowl then it may be the shock absorber springs on each corner. Try bouncing bowl up & down. If it feels weak then the springs will need replacing.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix washing machines.