Most likely anything with a pulley. Since we have no idea what year or engine you have there's no way we could even guess. A real location will tell us if it is right side or left side.
Great news is you can go out and figure out the culprit yourself.
Two courses of action. Remove the belt and check each of the pulleys for smooth even movement. Your other choice is to remove the shroud and while the engine is running and the noise is present spray lithium or other lubricant at the centre of each pulley. If the noise stops then you have a dry sleeve or bearing. Naturally the first route is much safer.