Some audio applications will take exclusive control of an audio device's drivers so that other apps can't play any sound at the same time. This is known as "Exclusive-Mode" and to deactivate it:
- Right-click on the speaker icon in the system tray and select Playback devices
- Select the device you want to listen to Audible with and click Properties
- Under the Advanced tab, uncheck Allow applications to take exclusive control of this device.
- Click OK to save your device's settings.