Must be a worn agitator drive block
or a broken anti wobble
If the splines wear smooth the agitator will be loose and the clothes
won't wash right, if the hub boot anti wobble is gone then that could be the noise you hear.
You gotta get the old spline out. I use a steel rod with a hook on it. To install the new one you need to weigh 350 pounds and have a nice tool to shove the new drive block in place, I use an old jack hammer chisel point. I apply rubber cement to the spline and invert the agitator to the floor. I use a piece of one inch all-thread to line up the spline so it won't go back crooked and I use the large metal jack hammer tip to force the spline all the way into the agitator. Sooner or later Larry will bring one by and I will try to take some photos of the operation. I used to charge $10 to install a spline at my appliance parts store back in the day.