Turn off the water to the toilet.
Does the tank lose water? If so, it may be a bad flapper making the fill valve work overtime.
If the tank doesn't lose water but the sound stopped, it may be a bad fill valve.
Turn off the water to the toilet.
Does the tank lose water? If so, it may be a bad flapper making the fill valve work overtime.
If the tank doesn't lose water but the sound stopped, it may be a bad fill valve.
The hum doesn't sound anything like that, but more like camping in the desert in the night with an idling diesel engine a mile or so away . Besides, the hum cannot be recorded with a microphone -- been there, done that.
It does sound sorta like a cricket. It's strangely familiar... like something with an almost dead battery, or some power bricks.