Why does my Audi A4 make a squealing noise when I turn on the AC?

I've noticed that when I turn on my AC in my Audi A4, there is a high-pitched squealing noise that comes from the engine. It goes away after a few minutes, but it's quite loud and concerning. What could be causing this issue and how can I fix it?

The most likely cause of the squealing noise is a loose or worn serpentine belt. When the AC is turned on, it puts extra strain on the belt which causes it to slip and make the noise. You should have your serpentine belt checked and replaced if necessary.