I haven't seen that warning but I found it by searching through the code. It looks like that will only happen if you're using the old XAudio based audio system. If possible I recommend using the new UE4 AudioMixer, it has more features and better plugin support. It should also fix that warning you're getting.
To enable AudioMixer add the following to /Config/Windows/WindowsEngine.ini
AudioDeviceModuleName=AudioMixerXAudio2More info on getting started with the audio engine here: https://forums.unrealengine.com/development-discussion/audio/116874-new-audio-engine-early-access-qu...