Lowering the volume of VO and beeps when unlocking FileVault

Hey everyone,

I've just upgraded to one of the new MacBook Pros with touch bar.

I have been using FileVault for years and it seems that, on the newer Mac models, VO has limited speech to guide through unlocking FileVault at startup. For example, it asks for the username, then the password. The beep indicators are still also present.

One issue I'm finding is that both the VO hints and the beep indicators are extremely loud, although my internal speakers are set to a fairly low volume. I have no other speakers connected.

Does anyone know if there is a way to change the volume of VO and the beep indicators when unlocking a FileVault-encrypted volume?

Any help appreciated.