My mate's Golf stereo had been playing up after he left it out in the snow last winter. The volume was sometimes muted when he turned it on, and his line in (from his Pure DAB radio) was poor quality and needed to be turned right up to hear anything. So he asked if I could connect up VCDS and see if there were any problems. We scanned everything, found a couple of faults relating to doors, cleared them, had a look in the basic coding options for the MFD 2 Sat Nav/stereo (that put it into diagnostics mode) couldn't find anything obvious and left it at that. That fixed both his problems! No idea how.