[en] Extensive research has been carried out over the years to reduce the acoustic noise resulting from vibration of electromagnetic cores mainly caused by magnetostriction. This paper presents the results of a basic experimental study of magnetostriction in strips of grain oriented electrical steel commonly used in electromagnetic cores which gives an important new understanding of the phenomenon. Results suggest that a transformer core assembled from laminations of grain-oriented electrical steel around 0.3 m long would resonate at a magnetising frequency of 1.5 kHz which could result in excessive vibration and noise