To check that the sat nav is emitting sound, do the following:
Open the device's main menu and select "Settings”. Choose the option for sound and check the volume level. Then check the settings in the NDrive software (Menu > Settings > General > Volume) since the sound can also be changed by the software.
Note: NDrive sells its software to several OEM partners, which may use sat nav models with specific settings. Please, always refer to the local support center if you need assistance regarding hardware.