The sound of the future (at least from an ambient perspective) is both about sound intensity and sound character. Cities will always have the same kind of noise soundprint, comprised of the various sound elements that typify a city. New materials will make different transient sounds, like the close of a door. There are the future-retro sounds that we already know, and that might be a part of it; but the sound of the future will probably be much quieter, at least from an intensity perspective.
The new SF trends in film have the future looking similar to now or perhaps five years into the future. The films Her and Transcendence use this approach.
There may be a burst of innovation at some point, at which time we'll experience a 1950s redux that will resemble then1950s in the 2030s as much as the 1950s resembled the 1870s.
But this could simply be the trope of continuous progress. Perhaps progress only has so much steam to propel it into the future, or once you arrive at a future you decide that it is good enough.