Yep, I should have mentioned that I suspect it was related to the rear climate control.
You hear it mostly when you brake, correct?
2013 Mercedes-Benz ML63 AMG Loaded
2011 BMW 750Li Carbon Blk Metallic, Oyster/Blk Nappa Leather, Ash Grain Trim, (Camera, Cold Weather, Driver Assist, Luxury Seats, M Sport w/20" Wheels, Premium Sound, Rear Entertainment Pkgs), Integral Active Steering, Instrument Panel w/ Leather, Ceramic Controls, Head-up Display, Smartphone Integration, Combox
2004 BMW 745Li Titanium Silver, Black Leather
Former: 2008 BMW 750Li, 2001 Audi A6 2.7T, 1998 Ford Expedition, 1993 Lexus ES300