Several things could cause this:
* Low oil level: The most obvious cause. Check your oil level immediately. If it's low, add oil of the correct type and weight (check your owner's manual) and see if the noise and light go away. However, even if adding oil temporarily fixes it, you still have a leak to find.
* Oil pump failure: The oil pump is responsible for circulating oil throughout the engine. If it fails, oil pressure drops, leading to the clattering (metal-on-metal contact) and the oil light. This is a major repair.
* Worn bearings: Low oil pressure causes bearings (crankshaft, connecting rod, camshaft) to wear down and eventually fail. The clattering is the sound of these bearings failing. This is a very serious and expensive repair.
* Oil cooler leak: An internal leak in the oil cooler can cause oil loss, leading to low pressure.
* Clogged oil filter or pickup tube: A blocked oil filter or pickup tube restricts oil flow, reducing pressure. This is less likely to be the sole cause of the problem, but could contribute to it.
* Leaking oil seals: Seals around the crankshaft or camshaft can leak, reducing oil level and pressure.
Do not continue to drive the car. Driving with low oil pressure will cause extensive and irreversible engine damage. Have the vehicle towed to a qualified mechanic for diagnosis and repair. Ignoring the problem could lead to a completely destroyed engine requiring a rebuild or replacement.
