2011 Malibu 2.4 liter flex fuel 6 speed automatic transmission. When my window is down and am idling. I hear this rattle noise that sounds like it's coming from the driver side. But I pop the hood and leave it idling it sounds like the passenger side. I notice it more with ac on. But when I listen for both sides while looking at engine it's fine without ac on. Doesn't sound noisy at startup and no check engine codes. I just hope it's not a timing chain/ tensioner. Car has 129000 miles on it. Thoughts? I hope I'm making sense.