This is the Whirlpool made equivalent of the Large Capcity Thin Twin Laundry Center.
Sounds like something may have worked its way into the pump. You'll need to remove the washer cabinet to get to the pump. I would take the drain hose from the wall and lower it into a bucket to draw off the tub full of water first, as you will be taking both hoses off the pump.
You'll find the service manual HERE