It's without a doubt the LED's themselves. Moving closer to the exact location of the LED confirms it.
For some cheap products, I've physically cut one side of the LED pin to shut it up, and the buzzing stops.
Though technically it could be the sound of a capacitor charging/discharging or the resistors, not exactly sure on the exact mechanism, but it's at the very least something on the LED circuit.



I'll take some metalocalypse mixed with metalocalypse
Gimme s5