2011 Range Rover tdv8 intermittent sound on radio

I have a 2011 tdv8, when listening to the radio and turn the vehicle off the sound does not work on the radio, however, the next time you turn it off and on the sound starts working again, this is very random. The sound comes back on when I pressed the mute button on the steering wheel and then after 2 mins will go off again.
I have searched Landy zone forum for the answer and found, the sound problems are all from older models up to 2007.
I don't know if they made any modifications to the face lift model to prevent the water ingress to the Amp.
Could this be the same issue as the pre face lift models, with the Amp?

I'd check for water & corrosion in the rear nearside quarter.