I stood under the transmission lines with my Olympus LS-7 recorder in NW Ohio to get the sound. According to a map I found online, the lines are indeed 765,000 volts phase to phase, four lines bundled for each phase.
765千伏輸電線路嗡嗡作響
聲道：2
類型：wav
power、voltage、electrical、hum、high
功率、電壓、電動、哼、高
資料來源：freesound ( https://freesound.org )