I am preparing to roll out the Hum Map and Database survey form in Chinese, thanks to Pattie from UBC.
But another idea just occurred to me: China has an excellent historical record, going back thousands of years. I would expect this has been digitized and exists in a searchable format. If you can read Chinese and have access to such an archive, perhaps could you spend a few hours searching through it, looking for evidence of the Worldwide Hum. You may need to get creative in your search terms because, obviously, modern machinery and electronics are only a few hundred years old, and therefore descriptions of the sound might rely on similes from nature. Please contact me at email@example.com if you find anything.