Isn't that most cars though, and not saloons?
I probably should clarify when I say cars I mean that as in "vehicles with 4 wheels", i.e. I include, SUV's, CUV's and pickups in the mix, not just saloons and hatchbacks. Lift the vehicle off the road a bit more and you loose a lot of the road noise inherent in saloons and hatches, one of the reasons the E-Tron is quieter than the Tesla S and 3. Personally, the quietest cars I've been in are Crossovers and (North American) pickup trucks (and that includes vehicles like brand new MB E Class and other saloons).
Cars with diesel engines do have an inherent disadvantage too (i.e. most 5 series)
EDIT:re reading your comment, yes, you're right in some senses. I was to broad in my initial comment. It's very car model dependant and while there is a correlation, specific noise levels aren't directly related to specific classes of car.