You notice the hum of the air-conditioner when it comes on and when it goes off – but not in between.

空调开启和关闭的时候你会注意到嗡嗡的声音，但在运行中你就很少注意到。

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If you're walking indoors, notice the sound of other people talking, the sound of footsteps and the hum of lighting fixtures.

如果你是在室内行走，留意人们的说话声，脚步声和照明灯具发出的嗡嗡声。

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By comparing the intensity of the hum with the height of waves around the world, scientists can track where the buzz is coming from.

通过把全世界海浪高度和嗡嗡声的强度相比较，科学家能追踪到这种声音的来源。

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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

If you want to hum the piece quietly to yourself, that's fine; that's good.

如果你想自己跟着曲子,小声哼哼,没问题,那很好

耶鲁公开课 - 聆听音乐课程节选

The hum of improvised conversation, the rustling of newspapers turning, the clinking of cutlery.

BBC: Vienna��s recipe for living well

Giant lathes and centrifuges surround our metallic table, and the hum of machinery fills the air.

FORBES: How Nathan Myhrvold's Modernist Cuisine Became The World's Most Influential -- And Profitable -- Cookbook

We did notice, however, that the mic was able to detect the hum from our MacBook Pro's fan.

ENGADGET: Blue Microphones Tiki USB microphone review: a thumbdrive-sized mic for mobile recording