A metallic buzz at idle from the turbo. The actuator linkage has play.
Worn wastegate linkage or a tired actuator letting the flap flutter.
Annoying more than fatal. Have the linkage checked at the next service.
Reading about sounds only goes so far. The tuner on our home page listens in your browser and tells you what it hears. The app goes further: it names the exact fault, checks it against your vehicle, and tells you how urgent it is.