Hum-buzz

Speaking so quietly I was confident the ambient hum-buzz and the trio of phone conversations would keep anyone farther than a foot away from eavesdropping.

[...] you'll end up in the Backrooms, where it's nothing but the stink of old moist carpet, the madness of mono-yellow, the endless background noise of fluorescent lights at maximum hum-buzz, and approximately six hundred million square miles of randomly segmented empty rooms [...]