I've got a 2015 Yukon Denali and have experienced the buffeting noise as well. I found that when it starts buffeting i set the cabin thermostat up 1 degree to get the heat/air to kick in. As soon as the heater fan kicks on (low) the buffeting is gone. It has to be a cabin pressure issue for me. I'm currently stationed in Grafenwoehr Germany where the weather today was 27F.