The working frequency of the internal components of the power adaptor is within the audible frequency range of human ears (20 Hz to 20 KHz). People with sensitive ears may hear this noise. This can be avoided by unplugging the power adaptor when it is not in use.Every adaptor has undergone rigorous safety certification and testing. The noise is generated by the normal operation of the product and does not affect product use or pose any safety risks. Please use it with confidence. If you have any further questions, do not hesitate to contact us.