Much quieter than my 1984 Rabbit Diesel
At idle the Rabbit's dash would vibrate so violently and the plumes of black smoke it emitted were just noxious. I got well over 45mpg tho...
It is definitely a little more 'chunkier' sounding but at speed it's not that noticeable and most people that ride in my car are surprised it's a diesel when I tell them. Plus when you need power it's just there and flat out hauls azz.
I have a friend with a 2009 X5 3.0si and on a recent ride in it (in the back seat) it's definitely quieter and IMHO a bit more sportier sounding.
FWIW - I just towed my ski boat for the first time this weekend and the diesel engine is amazing! I have to tow uphill for quite a distance and the car just keeps accelerating like there is nothing behind it.
The engine sound has grown on me.