Whenever my engine reves, there is a loud and annoying screeching sound that comes from the engine. I believe it is either the idler pulley or the alternator; somewhere around there. It is especially evident when it is wet outside or when it rains. Otherwise it doesn't really make much noise. I tried putting some dishsoap (like a friend told me to do) on the belt and that works for a little bit but it comes back. Any help?

If the soap helps, it's probably the belt. When you have the belt off, check the idler pulley and belt tensioner. They should both rotate smoothly and quietly with no wobble.