Watch the octane rating of the fuel you use. In some parts of the country, regular is 85 octane. I've found that I get that same symptom with my '06 if I use 85 octane so I step up to mid-grade at those stations which is usually 87 or 89 octane and the issue goes away. The bulk of the stations out west are 87 octane for regular.I don't know if it is the fuel injection or the valves, but I have noticed that when I accelerate agressivley I notice a rattle in the engine, not a terrible sound but noticeable. I have a 2003 with 50K, any ideas or suggestions?