How to disable the audio output of Gnome Boxes (or at least mute all sound)?

Most desktop environments and distros use various alert sounds, can be distracting when you have a high-end sound system connected to the computer and some ~0 dBFS bell jingle or a generic error sound plays. At the time **I don't need any audio in my virtual machines** — it's preferred to entirely disable the sound processing, if possible. I'd appreciate not having to ever configure the audio setting in a fresh VM (be it alsamixer, pactl for Pulseaudio or DE settings). The Gnome volume mixer (settings → sound → volume levels) doesn't appear to save the muted state even for one VM.