Peugeot 406, Clarion Radio/CD Player - No Sound?

I have a Peugeot 406 Saloon - HDI Diesel 1900cc. This contains a Clarion Radio/CD Player.
For some strange reason there is no sound!!!!
The unit comes on in the normal way with all lights on, and when I put a cd in the cd player I can hear it loading. I can even select the memorised radio channels ok from the unit & the stalk. However, there is no sound from either the cd player or the radio???? All other units are working - interior lights, horn, indicators, fuel guage and so on, so I doubt if a fuse is at fault. I thought I might have a selected a "mute" button by mistake, but there doesn't appear to be one. I can see the volume display as a bar scroll, and see this increase on the unit as I turn the "ON" button in a clockwise direction - but still no sound!
Can anyone help/advise please.

Many thanks.