Definately sounds as if there is something inside the drain pump. The drain pump is basically an impellor that turns to pump out the water.
I have included an image of what the pump looks like and its located in the base of the appliance. follow the drain hose and that will lead you to it. You can seperate the housing of the pump to check inside. nb: remember to empty out all the water from inside before attempting to remove the drain pump.
good luck !