Timing that has wandered. Rough running with rattle. Needs a shop before it needs a new engine.
Worn phasers or actuators, chain stretch, or oil pressure problems feeding the timing system.
Shop time with a scan tool. Timing codes plus rattle is a now problem, not a someday problem.
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.