Do you have a rev dependent noise coming from your engine compartment? Here is how you find the source of it.
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Belt covers might also touch something, this is also a common noise source.
1) remove power steering belt, turn engine on, check for noise. If it's gone, check your belt and try to rotate PS pump - one of them is the problem.
2) if the source is timing belt covers, they might change the pitch or level of noise when you press covers using some tool. Be careful to NOT get your tools or hands into belts, you might loose your fingers this way! Do not wear a scarf or anything similar - it might get caught there, too! Try pressing covers. If this changes noise - the source is belt touching a cover.
3) remove alternator belt, turn engine on, check for noise. Only for several seconds - your water pump is also driven by the same belt! If this noise is gone - your source is either belt itself, alternator (it's bearings) or water pump. Inspect your belt, rotate alternator's pulley to look for any unusual clicks or resistance for rotation. Rotate your water pump to see if it creates any noise and unusual resistance.
4) Now its time to inspect your timing belt & tensioners. Remove all covers, look for belt and cover damage. Check if your belt is tensioned properly. If everything seems alright, you'll have to remove your belt and check tensioners.
