i need help: what is this noise ( from a pulley )

Does not sound like a belt to me! Sounds like a bearing is dry and is not far off seizing.

Take both belts off if a twin cam, I can't remember what belts single cam engines have. Then spin the alternator and water pump by hand and wiggle the pulleys to feel for play.

If one is tight or has too much movement in the bearing, it is your suspect.

The power steering pump pulley will be hard to turn so you'll only be able to feel for excessive movement.

Alternatively, spray wd40 into each one's bearings whilst it makes the noise running using the straw to stop it getting on the belt. If the noise changes, you have found your suspect.

If you think you need new belts or will buy a new one anyway you could spray wd40 on the belts to see if they are making the noise as it will stop but the belts will be useless after.

Kirkynut