So in the past couple weeks, I've noticed a weird rattle/flutter after startup on my 08 LS. It sounds like it's coming from the engine bay towards the right (from driver pos) and it only happens when I haven't started the car after a few hours. The longer I let the car sit before starting, the more it does it. I turn the car on and it lasts for about 2-3 seconds, then goes away. If I try to restart it, I cannot get it to duplicate. But if I let the car sit for a few hours it does it again. It seems to run fine without any problems whatsoever. Anybody know what this could be?