Characteristics of the local vibration modes of an aluminium extruded panel are investigated by the finite element analysis and modal testing. Practical methods to increase the damping of the local resonances are proposed. Effects by filling urethan foam in the core cavity and by coating tar on the panel surface are compared by experiments. Modified panel structures to shift the local resonance frequency band are proposed. The results of the study are utilized to predict the severe local resonances in the aluminium extruded panels and prevent their undesirable effect on the sound insulation.