You don't need to remove the tub nut to inspect the drive block. Just remove the agitator and look at the top of the drive block. Make sure the grooves in the drive block are good and engaged with the tabs on the drive tube. You should not be able to rotate the tub by hand easily. It doesn't sound like the drive block to me. Sounds more like either the brake cam driver is worn/broken or the spin gear in the gearcase is stripped. It seems pretty loud as if it's outside of the gearcase. This video, which shows how to replace the clutch band, will show you how to take the washer apart and remove the gearcase to get to the brake cam driver and see what a good one should look like. Here's a pic of a good drive block.

Eric

The brake cam driver is the white plastic piece in this picture. It is attached to the bottom of the basket drive and brake assembly with a C-clip. The tab on the driver extends down into the clutch hub. The clutch hub is driven by the gearcase in spin mode. The clutch band inside the clutch hub is held in place by spring pressure. A tab on the clutch band engages the tab on the cam driver and rotates it to release the brakes and rotate the basket drive. You need to make sure the tab on the cam driver is not worn down or broken.

Eric

You REALLY know your washing machines. The brake cam driver was the culprit. Just ordered a new one. Thank you so much.

Well, I'm thinking it's something with the gearcase. I notice that while the basket and agitator are spinning, the agitator periodically stops, or nearly stops, and starts again. The agitator shaft should spin freely during spin mode. The only thing that can really stop it is if the agitator gear in the gearcase engages the splines on the agitator shaft. During spin mode, the agitator gear is held up away from the splines by a cam assembly that is operated by a shift actuator. If there was a problem with the cam that allowed the agitator gear to start to engage the splines on the spinning agitator shaft, it would create the ratcheting sound and abrubtly stop the agitator shaft if it fully engaged. It appears as though the agitator gear is briefly and repeatedly trying to engage. With the agitator off, remove the metal clip and lift the plastic washer from the agitator shaft. Now with the tub spinning, grab just the splines of the agitator shaft with the rag. You should be able to completely stop it. If you feel it suddenly grab, then it is likely the agitator gear trying to engage. The agitator shaft comes up through the bearings in the spin tube. It is normally just the friction of these bearings that cause the agitator to spin in spin mode. The plastic washer and clip on the agitator shaft are only used on models with the fabric softener dispenser on top of the agitator. You will notice that one tab of the plastic washer goes down into the groove in the drive block and the other tab drives the clip. This ensures that the agitator spins at full speed during spin to force the fabric softener out of the dispenser. The other question is why did the small tab on the brake cam driver break off and what happened to the piece that broke? It's purpose is to keep the tab on the clutch band in place between the large and small tabs on the brake cam driver so that the clutch tab doesn't slam the cam driver every time spin starts.

Eric