Washer shutting itself off.

[Willow09]

We have a four year old Whirlpool Gold, Ultimate Care II washer that shut itself off last night at the beginning of the spin cycle (clothes were soaked but the water had drained). It made a loud buzzing sound that lasted much longer than it does at the end of the cycle. The buzzing sound stopped when the washer shut off. When we tried to start the load again the tub looked like it was agitating way more than it should have. Any idea what part may have broken?