I've never sat in the back seat while we are driving but truly there is no road noise in the front. My DIL drives for a living and that was one of her first remarks - lack of road noise on her Premier and how great that was.
Maybe different roads? We know road noise - we have had Corvettes - one was a convertible C5
that had lots of road noise .
I'll ask my son - he's a designer at GM. Only thing I've had him comment on is he feels the engine is noisy when you greatly accelerate - he's not sure that wasn't done on purpose.
My hub's negative is the brake and trans combo when coming to a stop but he's very sensitive about that stuff - son said he didn't notice it. Both of these guys are big time mechanical guys so they are looking out for stuff like that.