What is causing the squeaking from under the hood? on 2007 Mercedes-Benz C280 4MATIC

All of sudden getting a weird squeaking sound from under the hood, like a belt issue. Would belt dressing typically solve the issue or could it be something more?

Asked by for the 2007 Mercedes-Benz C280 4MATIC
It can be a belt, belt tensioner problem, bearing failing in one of the pulley.
I've seen failed air pump making similar sound, but it comes on while the engine is cold and will go away after a minute or so. I'd take it to a shop and ask them to diagnose it.