I have somewhat of a similar rattle coming from the front of my car, same thing, only happens when accelerating, as soon as I take my foot of the gas, it stops.
At idle, nothing at all. Been told that the heat shields may be the problem, but they all seem fine, I will have to double check them. Anyway, I hear it mostly at low speed, on takeoff and sometimes at highwat speeds(60-70). The sound itself is like something is loose or like a bird chirping.
Hope you find what the problem is and so do I