setting idle just slightly higher than recommended seems to help in this regard - every diesel is slightly different as to harmonics - but yes, they don't really smooth out until past 1800 or so, at least mine doesn't. The NorSea, like our Voyager, has an unusually long prop shaft and I have found proper setup/alignment is even more critical than some of the shorter shaft versions I have worked on. Like you I run a drive-saver at the transmission and consider it essential for our setups.