During a recent trip with my Suburban (Black 2013 LTZ, 5.3 Flex, 37500mi) I started hearing a grinding/hissing sound which seems to come from (generally) the passenger side of the engine compartment. I've put the truck in neutral and revved the engine, but the truck doesn't make the sound. Put the truck back into drive and accelerate, and it makes the sound again. The harder the acceleration, the louder the noise.

To me that seems to eliminate the exhaust system or the air intake as the sources of that noise. Are there known issues with the transmission or drive train that could explain this noise under these circumstances?

 

Moved the auto 4WD to 2WD and the noise went away.