Just pulled a tough hill, towing my about 17k 5ver, pushing it hard to get past a wide load truck and the turbo went to about 20,000 or so... pretty loud wind up noise that is new to me. Wondered if ...
Possible combo of boost pressure getting the turbo to sing, cooling fan kicking in (roar) and active intake management switching to fresh air intake to lower intake temps. Nothing wrong, you got a bad @ss truck!