inner wash basket thumping on fast spin

Washer spins fine until it kicks into fast spin, then the inner basket starts getting out of balance. After about 15 seconds the inner basket starts hitting the outer drum then it starts shaking around. This happens whether there are items in the washer or not.

Also, we notice in our book that the warranty covers the costs of an inner wash basket (parts only). Would that be for a part failure or maybe just rust?