It has the GM 3.6 LLT engine w/ VVT. It's a popular enough GM platform/Engine that I figured one of yall may offer some good insight. Some details: -The engine makes a loud rattling noise AT IDLE ONLY. The noise almost sounds like a knock, but it completely clears up when revved up. Say above 2-2,500 RPM. -Engine has ~110,000 miles.