A Pipe Flow generates acoustic noise when it develops a turbulence.
The turbulence is accompanied by density variation which creates pressure pulse propagation which is then called the acoustic noise.
The model describing the circumstances and the amplitude of this noise has been suggested by M.J. Lighthill in 1954 (see Lighthill equation).
See also
Physics / Mechanics / Continuum mechanics / Fluid Mechanics / Fluid Dynamics / Fluid Flow / Pipe Flow / Pipe Flow Dynamics