Honda makes larger inverter generators too. Here's a 5500/7000 watt model that runs at 52 - 60db. I don't see where B&S lists the noise output on theirs, so I'm not sure how that compares. http://www.northerntool.com/shop/tools/product_200640183_200640183The Honda inverter generators are really quiet and fuel efficient.
But they don't run at 240V which the OP needed for his well pump. Honda also makes regular 3600 rpm generators, but I'm not sure they are much quieter than the Briggs & Strattons, which have an extra-large exhaust.
Portable Generators for Camping and RVs '|' Briggs & Stratton