Mine is nearly nine years old and I have had this problem twice... both times it was for the same reason. I have taken it in to my local repair shop both times and the repair was pretty inexpensive... How it was explained to me is that the machine is shaft driven and the coupling from the shaft to the tub/agitator wears out (I constantly wash large loads, blankets, etc.) The replacement part is cheap, but I get charged for an hours labor when they fix it. It comes to less than $100 altogether for the repair.
Cody, October 2007