That's the thing. Common rail units are quite a bit quieter than the older tech engines. The PD VW TDI's, namely the 1.9 were noisy and rougher than the later common rails, but smooth and quiet at speed and incredible reliable.
My Audi has a 7 speed gearbox so at motorway speeds, around 70, it goes into top gear, brining down the revs and the noise. That goes someway to help with their fuel economy, The shorter range first 4 gears help with acceleration.