The timing chain can develop a rattling noise caused by failing timing chain guides. This is often due to extended mileage intervals between oil changes that allows the oil to become dirty and abrasive which wears away the timing chain guides until they fail. The timing chain and guides should be inspected at each valve adjustment, otherwise serious engine damage may result.
Rattling Noise From Front of Engine on Toyota Previa
Average mileage: 219,000 (219,000–219,000)
5 people reported this problem
Haven't fixed yet. However, I will have my valves checked and continue with the synthetic oil.