There are many different theories about the purpose of making noise. This article should describe a few of the different noise theories. One must note that which stance a person takes on noise is highly dependent on what they consider art and their ideas about what art should be. For the most part, people will either think of noise as being an extension of music, or as a force in direct opposition to music.
History of Noise Theory
Futurist painter dude Luigi Russolo was one of the first people to incorporate noise into music. He wrote a manifesto about noise and a paper about the theory of using noise in music. I'm not going to tell you about it because I haven't read any of it lol.
Noise as post-musical expression
Some believe that noise is the logical end of all musical genres. They feel that music and notes are short-sighted and can only tell a very limited story. This view of noise is more that the traditional structures of music are confining. This is different from experimental music in that instead of taking these structures to the extreme, they are completely destroyed. In this was an artist is free from musical constraints.
Some artists create noise as something with no influence from music whatsoever. Rather than a highly abstracted and extreme form of music, they see noise as a primal thing that came before music and is therefore perhaps more worthy of expression. Noise primitivism focuses on the fact that humans are bombarded with meaningless data constantly, as opposed to the post-musical idea of using noise as an inspiration.