The object of this paper is the study of the noise produced by inverter-fed three-phase induction motors with squirrel-cage rotor. A wireless sensor network based measurement system is proposed, which gives the possibility of measuring the sound pressure virtually simultaneously in multiple points around the motor. In the case of inverter fed motors, the phenomena that lead to the production of the magnetic noise become more complex and the motor becomes noisier because of the increased possibility of matching the exciting frequencies with stator natural frequencies. In order to evaluate the influence of the switching frequency of the PWM inverter on the overall motor noise, the noise-frequency level diagrams (spectrograms) have been traced for a two speed motor of 1.5/2.4 kW, 750/1500 rpm, with 36 stator slots and 46 rotor slots.