Sounds like an issue with the motor (worse case scenario) or possibly an agitator that is just slightly out of alignment (best case scenario). From your description, the most likely case is a worn out plastic coupler or cam. These are easily replaced and much less expensive than replacing a major part.
I would have a repairman (or better yet, a friendly and free neighborhood jack-of-all-trades) take a look at it. If he can remove the inner tub, he might be able to peer inside and save you quite a bit of money!
I've heard of loose or worn out bearings that caused the "clothes mover" to get loose from the agitator. This almost always resulted in clothes getting "suctioned" around the agitator.
Regardless, I would recommend contacting a good and knowledgable "jack of all trades" instead of an appliance repairman. Repairmen from places like Sears usually charge over $100 just to look at a machine + parts and labor to fix. This isn't comforting when the machine itself only costs about $300.
Hope this helps!
Jeremiah 29:11-13
Matthew 5:8
Matthew 11:28-30
Chris
August 2008