Have you adjusted the volume on the steering wheel while talking? When I picked my D3 up I called SWMBO on the drive home and she could hardly hear me, without knowing the reason I increased the volume via the thumb wheel and hey presto, job sorted
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Audi D3 S8 - 2007 - V10. B&O, Phantom Black, black and silver interior, and still completely standard with everything working as it should
Audi TT - 2015 - Ultra