2003 Toyota Camry Rattle Engine Does Idle Moving Stops Couple Days After Oil

Rattle in Engine. Does it in idle and when moving. Stops for a couple of days after oil change. Use synthetic oil. Its not a continuous rattle, but most of the time.
Certified mechanic done analysis. Timing chain loose. Fixed. Did not stop the rattle. Now believe it may be timing chain inside the engine. Will cost $500.00 to explore and fix. If not the timing chain, he says the engine will need to be replaced with a rebuilt model-$4500.00. What do you think