The hum of the spinning blades is the sound of China going green as it seeks to address the growing energy demands of its rapidly modernizing consumer society and fast-paced industrialization.

VOA: standard.2010.08.03

And perhaps the explanation has got to be the ubiquity of death is this kind of background, constant hum.

也许应该这么解释，死亡的无处不在,是一种背景的，持续的嗡嗡声。

耶鲁公开课 - 死亡课程节选

just in a sense that when she was taking, say, I don't know, class like C.C., which is Contemporary Civilization, or Lit. Hum.,

就好像她在上论当代文明，或人类文学这样的课程时，我不太清楚，

介绍好朋友 - SpeakingMax英语口语达人