Not really sure that you can calculate the noise. Generally, there are empirical studies that show how much noise is generated at measured velocities. Then the ductwork/piping is sized accordingly to keep the noise level down.
See previous discussions on this topic on Eng-Tips - you can do a search on noise calculations. There is some attenuation from pipe wall thickness also.
Am not an insulation expert, but as far as I know, thermal insulation is not the same as noise insulation.