I have a 2015 Yukon XL with the cabin noise issue same as everyone else. Been to the dealer and they could not fix it. Dealer says GM is designing a new exhaust system or at least modifying the old one. Something about a baffle near the end of the exhaust system. Noise is terrible, worst around 35 to 45mph when it is in the 4 cylinder mode. If you put it in the towing mode which cause the rpm's to rise the noise goes away. Wife always buys the Yukon XL but I think this will be the last one. Especially since it is taking GM so long to fix it. A fix should have been figured out a long time ago, does not make sense.