I have a 2007 trailblazer 4wd and its got a rattle that comes and goes as I drive. I suspected a heat shield but couldn't find it, and just left it, but it occurred to me that the sound never happens in park or stopped at a light. The suspension has always been overly bouncy, but going over speed bumps doesn't seem to affect the sound. It happens on the highway, and I hear it most when I drive past a cement wall. It also happens in a parking garage going up and going down, fast or slow doesn't seem to matter.
This all leads me to guess it has to do with a differential or a pinion bearing. The rear one seemed solid to me. The front one seems to have a little rotational play but not up and down or left and right, but I'm not sure what it should feel like. I read somewhere to tighten the tension on the pinion, but I'm not sure that applies to me either.
I'm still hopeful its a heat shield, but it seems that it would rattle running it in park and be worse in the bumps. Someone else said its likely a baffle in the resonator or muffler, but I'm thinking that would rattle in park and worse over bumps as well.
I know with these things, sometimes its something that happens with all of them, and sometimes there's just no telling without having the truck up on a lift. Any thought?