A marble shake from under the floor. The insides of the cat have broken up.
A broken catalyst substrate shaking in its shell.
Expect a converter conversation. Check warranty first: emissions parts often carry longer coverage.
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.