My partners A1 is back working now after the retune. She also said there was no drop outs, which is remarkable considering how often it happened.
As someone with a logical mind, I can only think that there was a widespread issue with the transmission of the signal or a mistake with the 'frequencies' rather than with the radio itself. No-one has touched the radio apart from doing a retune, so it wasn't hardware related. I don't think Audi can do an 'over the air' update to any software either. I wonder if we'll ever know what's caused it?
