DIAGNOSIS That's almost certainly a problem with the drive system, and on this model, the most common culprit is a worn-out coupling between the motor and the transmission.
FIX You'll need to get underneath. 1) Unplug the washer and turn off the water supply. 2) Tilt the machine back carefully (get help, it's heavy) and put a block under the front to keep it propped up. 3) Look at the center where the motor connects to the gearcase. The plastic coupling has three spokes. If any are cracked or sheared off, that's your problem. 4) Replace the coupling—it's a cheap, common part designed to fail first to protect the more expensive motor and transmission.
IF THAT DIDN'T WORK If the coupling looks fine, the noise could be from worn transmission bearings or a failing drive pulley. A persistent grinding with a good coupling points to internal transmission issues.
HEADS UP Don't ignore this noise. Running it with a broken coupling can let the motor shaft hammer against the transmission input, causing catastrophic damage. Fix it as soon as you hear the grind.