I have this problem I haven't been able to solve. Under load around 2000+ rpms, I will get a loud whine until I let off the throttle. I have replaced the serpentine belt thinking the belt was slipping, but this is loud enough that I can feel the loudness of the while in the floor board when it happens. It's to the point where towing my boat up the slightest incline will cause this noise. I don't have a boost gauge but I can say it happens with either close to full throttle or at least high load/boost as I mentioned.
Here is a video of the sound from inside the cab. I have a manual transmission. I figured maybe the clutch was slipping, but I have never heard a slipping clutch make such noise. That and the clutch isn't all that old either. Maybe 70 - 80k.