I heard this long ago: The JT-9D, CF-6 and RB-211 were the first big fan engines, and the N1 blades went supersonic on takeoff, of course. That created a loud buzz saw sound in the cabin. The very smart Lockheed and RR engineers drilled and dressed the vanes and did everything possible to kill the sound at the source, and did a pretty good job.
The dumb and lazy Douglas and Boeing engineers just added a ton of sheet lead sound deadening to the cabin sidewalls, which was also effective. Lockheed would not did not accept that weight penalty.
At cruise, the Boeing and Douglas cabins were quiet, thanks to that ton of sheet lead, while the L-1011 was noisy...