Might just be the volume being very low.
If either Life or Essentials packages are used in your scene, check whether there are AudioAttenuation plugins placed on any AudioSources or Characters. That plugin has a separate volume slider for VR. As for the headset I had at the time (Occuls Rift CV 1) the volume is significantly higher, I made the default quite low. I made a survey at the time and a lot of people had that issue. Using other headsets or non-standard headphones the volume might be more normal, so you might not hear anything.