Scenic 2 Radio Fault

For the last week, each time we start the car for the first time, the drivers side front speaker makes what can only be described as a loud F*rting noise. Once stopped everything works normally. No distortion, no crackles, hisses, pops etc.

Has anyone had this before? Gut feel is damp or cold.

This is an Update List radio.

Seems I have some investigating to do on Saturday :(