[zawy]

Quieter means more energy is possibly available for more thrust. I noticed SpaceX rockets sound a LOT more quiet and smooth compared to older rocket videos. Notice upward tilting winglets on the tip of large airplane wings these days are to reduce the same vortices that are seen on propellers (wings work on same principle as propellers) in order to be more efficient and more quiet is just a side effect.

[ilyt]

Might be but they're not mentioning efficiency at all, which you'd think they would if that was the case (more efficient AND quieter would be even bigger selling point)