G650 Cabin Noise Complaints??

Nice C-206: 30% more horsepower than stock, probably leaps of the water and climbs like a homesick angel.
(I flew them with the stock 300 hp Continental, good airplanes)

As for quiet: MD-80 cockpit: I didn't fly them for living, but used to commute on AA's MD-80s from LGA to DFW:
Coming back from an all night Tel Aviv to JFK against the headwinds we landed @ 05:00. I would jump in a cab to La Guardia and bum a ride with the AA pilots
to Dallas. After being awake for 20 hours I would always fall asleep in the jump seat , head hanging down when strapped in by the shoulder harnesses and drool on my tie. Happened every time because the MD-80 cockpit was so quiet, even the take-off didn't wake me up.

The B-747 cockpit was fairly noisy, probably because the airflow sped up a bit creating wind noise, also plenty cooling fans and even a sextant port in the ceiling next to, or in the overhead escape hatch.
(Some pilots would pull the sextant port to smoke a cigarette and suck out the fumes, or so they claimed)

Back on topic, never been in a G-650 or any VIP jet, but got close to a G-II in flight school, 1978. (Skinny back then, before I became Americanized)

Noisy cockpit:



Also noisy:


Americanized Captain in noisy cockpit: