Not suggesting you soak the belt. On a serpentine belt system the top side of the belt will ride on some of the pulleys and the bottom side will be the tension side.When the belt gets worn or dry it will start a chirping noise. All the lube will do is help identify if the belt is the cause of the noise. Just one little skirt will either change the pitch of the noise or eliminate it all together. If it has no effect on the noise you can safely eliminate it from the equation. By all means don't drown the thing with lube. The only reason I said WD40 was most people will have a can laying around the house. Would I use it as a dressing.Not a chance.
Tim