I've got a D400 which is a non-towable Duogen - same blades and generator but not the gubbins in between. Compared to other units of a similar output i've been any where near it's much quieter. There's an air x on a boat the next pontoon down from me (about 30m away) and it drives me bonkers...

as others have alluded to it really depends on what stuff you're running, how large your battery bank is, and what weather you'll be expecting/ where you are going. A combination of charging methods often works well - wind/water/solar/alternator etc.