This paper presents an initial state of the art about the estimation of the sound power emitted by electrical machines. The paper proposes a new method, more accurate, to evaluate the sound power emitted by a PM machine by a 3D FEM mechanical analysis. It also takes into account tangential forces applied on the teeth. Finally the papers shows the impact of any harmonic force in the global emitted sound power in order to establish the most disturbing force. It proposes a guideline for active and passive noise control.