I have test driven every model of this vehicle in the past week, and all of them have had this rumble. Today I drove a 2015 Yukon XL that I had hoped to buy. I set the cruise at 60 km/hr and watched what happened. When the engine switched to V4 mode, the rumble began. I think that the problem occurs at 1100 rpm in v4 mode. I am sure that it is a resonation occurring in the drivetrain due to the engine lugging at low rpm, and ends up sounding as a rumble in the drive shaft or differential. I was extremely disappointed by this as I was set to buy. I set the cruise at 70 km, 80 km , same thing ... a rumble started whenever the engine switched to v4 mode. Very glad that I drove again. Now I will not buy this vehicle. It's not wind noise, active noise cancel , or loose roof liner, its resonation due to engine lugging. Switching to tow/haul or manual stopped the problem at these low rpm.