mystery problem radio cd player peugeot 306 2001

I have a very peculiar problem with the radio cd player in my peugeot 306 meridian diesel estate 2001.
When you switch on the ignition the radio comes on and does everything it supposed to do but no sound!
If you take out the speakerwire connector at the back of the radio with the ignition on or the engine running they work and the sound is fine.
When you swith of the ignition and switch it on again the same thing happens the radio comes on fine but no sound unless you take out the speakerwire connector and put it back again.
I am absolutely baffled why it would do this, according to the handbook connector B has a telephone mute connector but it is not fitted on mine just the normal 4 wires .
Its not the radio itself because I have another identical peugeot 306 and it works fine in
that one.
Is there somebody who can give me any clue as why this is happening?