There are multiple symptoms of a bad timing chain, but none of them is as obvious as a rattling that can be heard from the front of the engine, especially while the car is idling. The rattling is most prominent in engines with overhead camshafts.
The sounds heard from the front of the engine are caused by the timing chain beginning to wear and becoming more stretched around the camshaft gears.
Another common symptom involves shards of plastic that are visible in the engine oil. The plastic pieces coat the teeth of the camshaft gears around which the timing chain links.