In or for a computer mouse, an insert which fits inside a mouse cavity that, at the same time, readily accommodates the actuation of mouse buttons while not interfering with other moving parts inside the mouse. Accordingly, the insert would preferably occupy space within the cavity to reduce the free volume of space that would otherwise amplify a clicking noise from one or more mouse buttons, while also serving to actually dampen the clicking noise. The insert can preferably be custom-designed as to accommodate essentially any mouse design and thereby fit readily within the otherwise unoccupied interior space of the mouse body. Preferably, the material employed for such an insert may be embodied by a sound-dampening foam.