Please follow the procedure below:

1. Check the Microphone Mute function is not activated.
2. Check that the microphone sensitivity adjustment on the docking station is set to the appropriate setting for the telephone in question.
3. Check that the headset microphone is positioned correctly near your mouth.
4. In case of "humming", your phone might be very sensitive to radio frequency signals. Move the docking station and mobile units farther away from your phone.