turbo wind down noise after engine stops on shut off

on our Mack E7 upon shutdown as soon as the engine totally stops, then there's an winddown noise that sounds exactly like a starter winding down from full speed to a stop. It takes several seconds for the noise to stop. We haven't had this truck very long and it's done it everytime on shutdown. For a while I was afraid maybe the starter was stuck engaged, but that would burn up the starter very quickly so it's not that. It has got to be the turbo winding down but i've never heard one this loud. On our 6NZ C15's, we notice no turbo wind down noise on them, so why is there on this E7? Is the turbo on it's way out? It's a non-wastegate turbo if that matters. We don't have a boost gauge on the truck, so no idea how much boost it's producing but the turbo does still work. You can hear it spool up when pulling a hill and accelerating.I'm just concerned about the wind down noise. Should I be concerned?

 

By the time I get it backed into it's spot, then i have slowly moved it around the yard to dump the load, etc and once i park it, i sit for about 30 seconds at idle before shutting down. I'm just concerned as to how loud the turbo sounds as it's slowing down to a stop once the engine shuts down.

 

it still makes the exact same noise if i dont shut it down and the idle timer shuts it down....

 

It's a Mack engine (E7) and it isn't a VGT turbo. it's a plain jane, run of the mill normal turbo. there are no electrical connections anywhere on it and no wastegate.