Several years ago I reported on the research from Frosch that suggests the Hum and Otoacoustic Emissions (OAEs, or SOAEs) may arise from the same mechanism. One piece of evidence for this is that both the Hum and OAE are usually disrupted for several days by air travel.
I don’t know why I didn’t pursue this earlier, but OAEs can be recorded, even in newborns, using in-ear microphones. Here are some examples: http://www.otodynamics.com/supporthome.asp?CatID=2
Therefore, if the Hum is a type of auto-generated emission, we should attempt to record it. The microphones used in OAE testing start around $500.00 and go up from there. I haven’t got the funding to conduct this, but if a motivated reader does, s/he could secure a place in history by being the first person to record the worldwide Hum. If the experiment fails to record the Hum, that would be an important finding as well.
Let me know if you intend to conduct this experiment.