Did you get this fixed?
I seem to have the same/very similar problem.
Climbed into my A3 with factory fitted rnse turned the radio on and no sound came out. It appears to be functioning totally as it should just with no sound and intermittent popping of all speakers...
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I drive an A3 quattro sport sportback on a 55 plate after parting with a much loved Mk4 gti. My wife drives a mk5 gti which we want to change for an A6 avant tdi. Want to buy one? Get in touch!