When playing on all revealed, I found out that some sounds don’t reproduce if you aren’t in range of the sound source (being able to see that area in particular with units/buildings).
I’m not sure if this also applies with “Spies”, only found out it happens with the “All revealed” settings.
In the example above I’m using an AI to play for me and I start seeing parts of the map where I should not have vision (without the all visible setting) and no sound plays at all (excluding galleon bolt impact sounds).