if only one window is down it will make a weird noise. :)
It's called the "Helicopter effect" Most SUV's exhibt this when only one window is down, it has to do with the air pressure in the cabin. You must crack or open another window to eliminate or subside the effect. If I have the driver window open, I usually crack the rear passenger side by and 1" or so, so you get some cross ventilation.
try opening another window & see if that works. if only one window is open you'll hear a weird noise. hope that helps :)
there is nothing wrong with the car- when you open the window you change air flow- it will still do it some with 2 windows open (I drive one).
Looking for a Used Terrain in your area?
CarGurus has 21,809 nationwide Terrain listings starting at $8,495.
Search GMC Terrain Questions
GMC Terrain Experts