Recent tests show that Cummins is the quietest generator for residential homes.  Here is a homeowners video showing how quiet a 20kW whole house generator is.   This was installed in April of 2016 in Bryn Mawr, Pennsylvania by Colonial Generators.  Cummins is a pretty quiet company.  They are, by far, the biggest generator company in the world and while most of the generators for commercial applications they have a robust and growing residential business.   Great technology – they build all of their own parts, and a focus on longevity and sound.   They offer home generators from 7 kW up to 60kW.