Diagnosis
The shipping bolts were not removed, or the self-adjusting leveling feet are not set. The WT7900HBA has four transit bolts securing the drum for shipment.
How to Fix It
Turn power off. Tilt the washer back and check the rear panel. Remove all four shipping bolts with a wrench or socket. Keep the bolts. Insert the provided plastic caps into the holes. Use a wrench to adjust the four feet until the washer is perfectly level front-to-back and side-to-side. Use a carpenter's level on the top rim.
If That Didn't Work
The load itself may be severely unbalanced. The washer can correct minor imbalance. For a single heavy item (rug, blanket), cancel the cycle, redistribute the load manually, and restart.
Heads Up
Operating the washer with shipping bolts installed will cause catastrophic damage to the suspension and tub. This is not covered under warranty. The bolts are only for transit.