The humming sound you're noticing is known as inductor whine or coil whine, which is a common phenomenon in many electronic devices that use high-frequency components, including chargers. This sound is produced by the vibration of components (typically inductors or transformers) when electricity passes through them at certain frequencies.

Please rest assured that this sound is not a defect, nor does it indicate any safety risk or affect the performance or longevity of the charger. Many manufacturers encounter similar sounds in electronic devices, especially when the charger is plugged in but not charging batteries, or in very quiet environments.

Hope this clears the confusion. Feel free to contact us if you have any questions or concerns about the product. We are always here to help.