My first machine had a significant whistled once a iPad was connected. Under a load of two devices without loading or no whistle was heard.
The customer responded very quickly and friendly with a replacement unit.
This replacement is much more pleasant, but not perfect. Furthermore, with only one connected device is a buzzing noise to be heard. However, this is a lot quieter and more bearable. Given the good price and the ordinary charging power I will keep the charger. But would it not strongly recommended for use in the bedroom.