Yeah Muddy, that is def spool up noise....but you're right, typically not heard on a turbo setup like ours. I'd isolate which unit it is. I wonder the bearing condition of the offender. Usually, a turbo spools up with so little resistance that you barely hear it on the intake side but if the bearings are misfit or worn, the resistance will cause the shaft to speed up slower and the air to make more "noise" as it deflects off the vanes. It could also be something as minor as a loose clamp(my guess) or a heat shield or the like coming off, causing you to hear different sounds. My supercharger on my car has sound deadening devices on the intake side to cut down on that exact sound. I removed mine after 10 years because I kinda like it!
Happy New Year
jeff
I wanted to clarify....most turbos do not have "bearings", they have thrust washers/seals(think piston ring configuration) and run in an oil bearing. I didn't want to lead anyone to walk into their local shop and tell them they might need "turbo bearings" b/c they just might see you as a $$$$$! LOL
