I assume it's a top loader with an agitator paddle. Try turning the agitator by hand, then tighten the knurled knob at the top of the aggitator it may have come loose. If it still moves around freely then the nut holding the agitator clamp rod may have stripped its thread. and it will have to be replaced. Not a hard job but good fit socket or ring spanner is required to undo it. get another nut through the local suppliers.
My hotpoint top loader did the same. Mine used to nearly jump out of the top when it spun, so while waiting for the nut to be ordered I put the clamp rod through the aggitator turned it upside down and put some tape on the rod to bulk it and screwed it back in the nut it worked for each wash until I replaced the nut.
Bob, October 2005
