Peugeot 206 radio volume issue

When the radio is turned on, sometimes, after a few moments (sometimes immediately) the volume increases to full by itself! Also, turning it down by the radio control itself will not keep it to the set volume, I have to turn it 'down' by the stick/column arm control! And get this, if I turn it up by the stick control, it also will not stay at the desired level - so I have to turn up by radio, down by stick! Madness all round, any suggestions here, my ear drums can't take any more???