I have only flown on the 737NG family 3 times in my life, and only twice aft of the engine. And always a window seat. When seated aft of the engine I too thought that the NG
was louder than a 2nd gen 737, but only on takeoff.
I always attributed the additional noise to the more powerful engine on the NG
But last week I was on a 757 seated in row 27 and noticed something that may be a culprit to additional noise on the NG
that I would like to share.
. Initial cruise was at FL350. Encountered turbulence and went to 370 and later 390. Both times when we started to climb there was a noticable power increase. The interesting thing about it was the "rumble" seemed like it was coming from behind me, and of course I was already seated behind the powerplants.
Before I say anything else, I only have a basic understanding of how turbine aircraft engines work. That being said, I think some of the noise a lot of people are hearing is from the turbulent air exiting the engine and washing up against the fuselage. Now why would that have more of an effect on the NG
vs. 2nd gen 737s and the Airbus narrow bodies? Well I have a theory on that as well. First look at how the power plants on the Airbus 320 family are mounted a lot lower and away from the fuselage than that of the 737. So obviously the airbus would have less of this "washing" effect that I have proposed.(I haven't flown on an Airbus in about 6 years, so I am going off that it is quieter from the above posts) And when comparing the NG
to the 2nd gen 737, the NG
engine has a larger diameter and maybe physically moves more air I would think than the 2nd gen engine would. And maybe that difference is enough that it would be noticable.
What I said above is just what I have noticed as airline passenger and is just a theory of mine. But I thought I would get it out there so one of the reputable posters can comment.