Hi all. New to me 2017 GLS550. I was trying to adjust the tailgate opening height. The car had not yet been started today. I started it and walked back to the tailgate. Since the engine was cold, the idle was high. Nice exhaust sound that you don't get to hear much. Then the Idle dropped a bit and I clearly heard what sounded like a turbo whistle. Hmm. Then the idle dropped a final notch and the whistling went away. FYI I traded my '14 GL450 which had a turbo V8 but don't remember it ever whistling. PS in the photo....22 cylinders, 1,086 hp, 1,220 lb/ft, 14.7 liters. The law of large numbers especially when they all drink premium!

as well, but I don't ever remember hearing a whistle. Anything to be concerned about, or just a nice sound to enjoy for a few seconds.