I have a similar model. there is a filter in the bottom of the inside. it should be a round grey drain. it twists easily in one direction to unlock and then the whole thing lifts up (screen and all).
on the underside is a pre filter, check it to make sure it's clean. if not, clean it in the sink with some hot soapy water.
if that doesn't solve your problem it might be the pump like others have said.
if it does solve your problem regular maintenance cleaning goes a long way. every 3-6 months I run mine through an empty cycle on pots & pans with two tablespoons of powered vinegar and one tablespoon of powdered citric acid.