John Cage, 1937:

I believe that the use of noise to make music will continue and increase until we reach a music produced through the aid of electrical instruments which will make available for musical purposes any and all sounds that can be heard...Whereas, in the past, the point of disagreement has been between dissonance and consonance, it will be, in the immediate future, between noise and so-called musical sounds.

[By "noise", Cage meant found sounds. By "musical sounds", he meant...]

Wherever we are, what we hear is mostly noise. When we ignore it, it disturbs us. When we listen to it, we find it fascinating. The sound of a truck att fifty miles per hour. Static between the stations. Rain. We want to capture and control these sounds, to use them not as sound effects but as musical instruments... If this word "music" is sacred and reserved for eighteenth- and nineteenth century instruments, we can substitute a more meaningful term: organization of sound.