Cindy, what type of pipe is the exhaust made of? Regular carbon steel, aluminized steel, stainless steel?

Regular steel pipes can be cleaned with steel wool, or wire brushing, depending on how rusted it is. Light surface rust will clean up fairly well, but heavier rust will have damaged the surface of the metal. You can usually get all/most of the heavy brown rust off with a wire brush, so the metal is shiny again, but no matter what you do, the pipes will still develop rust again....just the nature of the beast.