A rattle from the front cover, worst on cold start. A stretched chain or a tired tensioner.
Chain stretch, worn guides, or a tensioner that bleeds down overnight.
Do not sit on this one. A skipped chain can bend valves. Get it heard within the week.
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.