It seems strange, but you should regularly clean the inside of your dishwasher. To do this; remove the bottom rack, then check and remove solid debris. Place the bottom rack back in and place a cup full of vinegar on the top rack. Run the dishwasher on the hottest cycle. Once complete, sprinkle some baking soda on the base of the dishwasher and run a short cycle. Your dishwasher should now be clean and grease free.