Noise generation caused by a three-dimensional fan rotor-stator interaction is calculated to investigate the capability of current unsteady Navier-Stokes codes to predict complex noise generation and propagation in a real fan rotor and stator. Issues and special cares for the calculation of acoustic wave propagation in the fan are described. Still effort for accurate prediction is necessary, but encouraging results showing generation of acoustic waves at the stator vanes and detail of reflection and transmission through the rotor blades are obtained.