This is how upcoming iPhone 8 Wireless Charging Notification Sound will be....

Buried in iOS 11, there seems to be a new sound file that could potentially be implemented when the rumored "iPhone 8" is released with inductive wireless charging capabilities. Highlighted on YouTube, the sound file is called "engage_power.caf," and it is distinct from the existing "connect_power.caf" sound file that's used whenever an iPhone is connected to a Lightning cable.

In the video below, the unused charging sound is compared to the existing charging sound in iOS 11. The new audio file provides a longer, more distinct sound that could perhaps be used to assure iPhone users that their devices are properly charging should the iPhone 8 indeed include an inductive-based wireless charging function as has been rumored.