On my way home with unloaded trailer from Seattle to Minneapolis, started to hear a faint squeal similar to a belt slipping, when under acceleration.

Checked belt/tensioner - no problems. Finally on a steep downgrade I engaged the exhaust brake (not normally used when empty) and the squeal was constant and definately boost related...

With doghouse removed, the squall is unbearably loud. Turbo is functioning normally under moderate throttle but noise occurs under acceleration and activation of exhaust brake. Power and mileage normal, no black smoke even under heavy acceleration with squeal present.

Not sure if its a bad turbo to intake seal or a bad wastegate, but the truck is going in Monday to get it addressed - a smidge under warranty expiration.