Chirpping/squeaking noise

I have a 2001 Ford Ranger, automatic, 4.0L engine, with about 84,500 miles on it. There was a chirpping noise coming from the fan belt, I put some belt conditoner on it. The sound stopped. Then about 5 minutes of driving it started making an even louder squeaking noise that get a little louder when accelerating. The belt looks to be in good condition. What could be the problem?