Subaru / Denso Touch Screen Satnav - No Voice ?

[V8RX7]

Hi, hoping someone can help,

I have a 2005 Forester with the factory Denso Nav which works perfectly but there is no sound.

I have turned the volume up in the settings screen but I'm wondering if there's a "mute" button that I've missed.

There is a pic of a speaker on the screen but pressing it does nothing.

Thanks