In some cases, you may hear audio when streaming media but not when mirroring.
This is most often related to the volume settings on the device. When streaming media we are only sending data, and the audio is controlled by Reflector. When mirroring your device screen, we receive audio from the device itself.
In this case, you may need to ensure that the volume is turned up on the device and that the vibrate switch is not set to silent when mirroring.