This.
I used to have to travel for work, and would find myself in different cities all over the world. One thing I invariably noticed while working in Europe, their cities at least as congested as ours (often more), is their traffic noise is so much lower than ours. I think they have differing laws with regard to tire construction and how much noise a vehicle can make.
Yeah, you still hear the very occasional hotrod or Harley, but overall... so much quieter. You really notice it when you come home, landing in Philly and walking out to the pickup lanes of the international terminal, how much louder all of our vehicles are here.
PS - Yes, I know many European cities have banned private cars from their city center altogether. But I am not talking about (just) those cities or districts, it's even noticeable in the fully-trafficked areas.