Squeaking engine

Recently the engine in my 1995 Windstar has begun making a very loud squeaking sound. At first it sounded exactly like the radiator fan was "tinking" something on every revolution. When I check under the hood though it sounds like it's coming from somewhere on the bottom of the engine. The sound speeds up and slows down with the engine rpms. I've checked my fluids and they seem fine. The sound is also not coming from the left side of the engine with all the pulleys and belts. Any thoughts?

Thanks!