The easiest way to tell if it's coming from the drive belts is to spray
just a little WD-40 or similar substance on them. If the noise changes or
stops, then you know it's coming from the belts. If the belts are not
cracked or otherwise worn, don't sweat it. Then, when you replace the
timing belt, replace the drive belts, too, since you will already have
them off the car.