I bet ya you have a sock stuck in the pump.
Unplug the washer
Slide the machine out from the wall about 2 feet.
Tilt the machine backwards and lean it against the wall
-use 2x4's to prop it up if you have to
pull the 2 clips off the pump with a screw driver and disconnect the 2 hoses
Inspect pump, and/or set the machine back down, and try to start it again and see what kind of results with the pump removed.
Before you start, if you have a wet dry vac, get it ready for when you disconnect the drain hose from the pump. You'll thank me later.
If not get a bucket and some towels handy.