Certain model M keyboards have speakers in them, possibly for audio feedback for the otherwise quiet keyboard. /s
>Until the late 4th-generation variants, most Model Ms have a 1.25" slotted, circular speaker grille in their bottom surfaces. Relatively few contain an actual speaker, however, which was useful only for sounding beep codes on older terminal systems. The most common P/Ns with speakers are 1394540 and 51G872, made for RS/6000 UNIX workstations.