While trying to solve etymological riddles, we often encounter references to sound-imitation where we do not expect them, but the core examples hold no surprise. It seems that nouns and verbs describing all kinds of noises should illustrate the role of onomatopoeia, and indeed, hum, ending in m, makes one think of quiet singing (crooning) and perhaps invites peace, while drum, with its dr-, probably evokes the idea of the noise associated with this instrument.