Why does my Audi A4's engine make a high-pitched whining noise?

I've recently noticed a high-pitched whining noise coming from my Audi A4's engine, but I'm not sure what could be causing it. It seems to occur most often when I accelerate, but sometimes it's present even when idling. Can anyone shed some light on this issue?

The most likely cause of this high-pitched whining noise is a worn or loose drive belt. It's important to get this checked out and replaced if necessary, as a failing drive belt can cause serious damage to your engine.

Another possible cause of the noise could be a worn out water pump bearing. This is a common issue in Audi A4s, and should be addressed by a qualified mechanic as soon as possible.