A tinny buzz at certain revs from under the car. A loose shield. Annoying and cheap.
A corroded heat shield vibrating at resonance.
A clamp fixes it in ten minutes. Confirm it is not the catalytic converter first.
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.