I have been breaking my head on this for a day and a half now.
I am running VirtualBox 5.0.20 r106931 in Windows 8.1. My Guest system is Lubuntu 16.04 LTS, and I have successfully installed the VirtualBox Guest Additions. Afer all this, I cannot hear any audio when running either a video in Firefox, or an mp3 file in Audacious on my Guest Lubuntu system.
I have tried all three Audio settings: SoundBlaster 16, ICH AC97, and Intel HD Audio. I have checked all of the sound levels that I can find, and none of them is set to mute.
When I am running Audacious, the app shows that sound is being played and when I run a video in Firefox, the PulseAudioVolumeControl likewise shows that sound is being played [through something called the CubebUtils Audio Stream].
Any suggestions gratefully received.