You can manually turn off the voice notification via mobile app:
1. Go to Menu | Settings... | Advanced Settings...
2. Press continue when prompted to do so.
3. Scroll down to "Send Command"
4. Type in "r03e00" the press send arrow ("0" is zero)
5. Go back to home screen (no need to press "Save")
To turn it back on, repeat the steps above, but, send "r03e01" instead.