* A low, continuous sound: "The hum of the refrigerator was a constant background noise."
* A state of being busy or active: "The city was in a constant hum of activity."
* A musical note: "The hum of the drone was surprisingly melodic."
If you're looking to make a specific phrase into a noun, you'd need to provide me with the phrase so I can suggest how to do that.
For example, if you have the phrase "humming of the engine," you could change it to:
* The hum of the engine: This is already a noun phrase.
* The engine's hum: This also works as a noun phrase.
Let me know if you have a specific phrase in mind!