It looks like there are a few things going on. First from photo 5 i think your der hanger is bent. The cage doesn't look like it's coplanar with the cogs. Then the der rotation limit screw should be turned in so the upper pulley clears the chain stays. The chain looks to be properly routed through the cage and around the cassette. Not sure what you mean by "like a snake", the cassette to pulley chain run looks right to me from what i can see. Does the chain rub on something? Well it does rub on the outside of the chainstay on the chain's return stretch, pulley to cage. Try putting the chain inside the stay. How did this happen? Did you install a chain? Best understanding and suggestions can only come from a complete description of previous history. Andy.