normal
During the working process of the charger, there will be slight vibration in the internal device, so it will emit a sizzling sound. When the mobile phone is working, due to the resonance of the capacitor, it will also produce weak sound, and there is a transformer in the charger, which is switched in the non-stop on and off action.
At the time of high-frequency switching, the coil beats up and down due to electromagnetic induction, and makes a sound, if you are not assured, you can buy a new one.
When using fast charging, there is a sound, which is not normal