Every slow cooker seems to have a hot spot in it. It is usually on the side opposite of the controls, or somewhere on the back part. From now on notice where food sticks on and gets crusty. Then use a foil collar to prevent burning and sticking. I like to use foil collars when I make a casserole-type recipe in the slow cooker...it ensures that the casserole will cook evenly.
Here is how to make a foil collar:
Layer and fold sheets of heavy duty foil until you have a six-layered foil rectangle. Press the collar into the back side of your slow cooker insert (or wherever your hot spot is); the food will help hold the collar in place during cooking.