I've had a noise since I bought my 03 Eddie V8. It sounds like metal in a blender, or marbles being rolled around in a tin can. (It is not detonation). I only get the noise when I'm light to moderately accelerating, in any gear. Once in high gear and the torque converter locks up, the noise disappears.
It sounds just like a heat shield rattle. I checked all heat shields, and even smacked most of the exhaust with a rubber mallet, looking for something loose. Smacked all 4 cats, thinking they might be busted up inside. Nothing. Not a single rattle in the exhaust.
I thought it might be a stretched chain in the transfer case, but I drained the fluid and don't see any serious signs of that either. I'm fairly confident it's not in the engine. The noise doesn't seem to get any better, and maybe only slightly worse over time (35k miles more on it now than when I bought it). What the hell is that damn noise????
If I floor it, the noise goes away. At idle, I can't hear it. It's only when I'm lightly accelerating, and before the torque converter locks up. It has to be something in the transmission or transfer case.