This study aims at minimizing the acoustic noise from a magnetic origin of a claw-pole alternator. This optimization is carried out through a multiphysics simulation, which includes the computation of magnetic forces, vibrations, and the resulting noise. Therefore, a mechanical model of the alternator has to be developed to determine its main modes. Predicted modal parameters are checked against experimental results. Based on this model, the sound power level is simulated and compared with measurements. Finally, the rotor shape is optimized and a significant reduction of the noise level is found by simulation.