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Aside from what others said about trying to quite things in the first place, as far as the resounance goes, sound resonates due to the sound wavelengths bouncing inside the container or cabinet and the size is just right to amke the waves amplifly on top of each other. If you change the size of the cabinet or volume in the cabinet, it will kill the resonance quite a bit (at least disturb it). Try putting in some large solid objects to change the volume, size of the cabinet and the resonance should dissappear. Now you still need to quite other things down also.