My car has been making a whining noise that comes from the engine.

What could it be?

It is loud in the mornings when it's cold and only happen around 1800 - 2400rpm under light throttle (the car doesn't make boost)
When the engine warms up you can hear it faintly. I was worried that it may be the turbo but the car still makes normal boost levels and holds as normal.

Has this happen to anyone else?
What are your thought?