This strange noise has appeared over the last couple of months and only ever happens first thing in the morning when unlocking car using the blipper button.

No warning lights are activated and Motorline Skoda dealers are as baffled as I am, once the key is inserted it stops.  Baffled????? Has anyone else had this happen? 

Octavia 1.6 tdi CR Elegance 2012

was the outside temp < 5^oC? It's highly likely that the car's letting you know it's cold outside. Does the clock show the temperature rather than the time?

Low battery warning.

 

It shouldn't surprise us that a Skoda main dealer didn't know.

 

The bong is sometimes accompanied by a written warning on the radio display.

Electronic bong or a mechanical bong?

My drivers door external handle sometimes sticks 'open' and makes a noise when it goes back to its closed position.

Thanks for the response, it was warning me of low battery as suggested, checked the radio status and visual warning shown