Hi…..I have bought an A3 2009 with 60k miles, and the radio only has output on the drivers side speakers. The previous owner said it was a radio fault, so I bought a like for like one (Audi), but it’s still the same! Any ideas what might be wrong or where to start looking? Thank you for any advise.

I had similar.  And also side impact crash sensor fault issue.

Turned out to be the loom wires broken in the door jam. Poor quality wires.

Whip off the door card and test the speaker with some old radio ?

Thanks Dan I will try this. It’s so strange that all speakers except drivers door are not working.

kindest regards, Steve

Strange maybe, nevertheless it's a common fault that can affect locks and windows as well.