406 audio problem, constant ticking?

I have a 1999 406 executive estate 2.0L 16v.
Over the past 12 months I have had a constant, regular ticking on the audio system, radio, cassette and CD. It's there whether the engine is on or not. It is not engine related as it does not vary with engine speed. The only thing I can link it to is the digital clock on the display facia. I may be going down the wrong road here, has anybody had the same problem?