I see that European regulations are 74 dB for cars, 80 dB for commercial vehicles. Diesel cars there are less than 1 dB louder than petrol cars. There are, of course, a lot of diesel cars in Europe, and many of those are mass-market cars at affordable prices.
So obviously it
is possible to make a reasonably quiet diesel light vehicle motor, at a reasonable cost. Is there some reason why US diesel pickups can't be quiet(er)?
Comparative analysis of noise emissions of new European passenger cars | Efthimios Zervas - Academia.edu