This is the first time I have read about a noisy serpentine belt on a 5th generation RAV or 8th gen Camry (same 4 Cylinder engine) either here or in the Toyota Nation forum. It certainly is not a common complaint or issue and 25k miles is very low to have it wear out. If you are sure it's the belt area of the engine making noise it could be the either belt itself is defective (or stretched) or one of the pulleys or even a bearing in the alternator is making the noise. Your best bet is to diagnose exactly what's making the noise and repair it--spraying additives or rubber lubes on the belt do nothing. If you are not covered by warranty, I'd remove the belt and examine it for wear, missing or ripped or damaged teeth. Belts are not terribly expensive so I'd just replace it. With the belt off you should spin the various pulleys or idlers and make sure they spin freely and easily with no noise and do the same with the alternator. Replace bad components. It is vaguely possible the squeak you are hearing is internal to the engine--the VVT mechanism or the plastic chain tightener mechanism for the timing chain--but this is very unlikely and those parts last for 100k and more miles. It is also vaguely possible but unlikely your squeak is from the A/C components or valves. Lastly, I had a 2003 Jeep Liberty and the serpentine belt squeaked whenever the temperature dropped below 25 F and the engine was cold. In the summer and with engine warmed up it did not squeak--just something to think about.
