On my GE top-loader, the agitator wouldn't agitate. I could turn the agitator by hand very freely. Turns out the agitator coupler was bad. Cost me about $25 to fix. Pull the agitator straight up (if yours is the same as mine) and it will come completely out of the washer. You will see a bolt on top of the coupler that holds the coupler to the shaft. Take out the bolt and the coupler will pull straight up, off the shaft. If the grooves are "worn down", then the agitator is probably slipping as the shaft turns the coupler. This could make some sound, initially, until it's worn down pretty badly. Replace the coupler and the agitator will work fine, again.