I had our Terrain for about 2 weeks and took it on a road trip over the weekend. While fooling around with the toys, I rolled down the rear windows at highway speed (100 - 130 km/h) and discovered a horrible noise that I can only describe as a "wind echo". The wind from the back windows would enter the cabin, vibrate and cause an unbearable thumping "echo". It almost sounds like the subwoofer in the back is on at full power, so I thought that it might be the noise canceling feature, but I have a SLE-2 V6 and from what I understand the noise canceling system is only in the I4. Am I correct with this assumption and has anyone else experienced this? I'm thinking it could be an aerodynamic flaw caused by the body shape and large fenders.