A lot of the newer diesels are downright quiet. Pilot injection and a smooth pressure increase vs. just a big chunk of fuel all at once and a pressure spike makes a huge difference. My girlfriend's '13 TDI Beetle, while definitely not a gasser, is no louder than a gasser with the windows up.

My 617 is noisy noisy, almost Cummins like jarring. None of the other 617's I've heard sound like that. Timing is perfect and it runs well otherwise, so I don't worry. I do wonder, though.

Edit: If anyone's in Oregon with a normal running 617 and would be willing to meet up and compare notes, I'll buy lunch or coffee or whatever.

__________________
617 swapped Toyota Pickup, 22-24 MPG, 50k miles on swap