Sorry if you've said elsewhere, but is this a genuine kit? Several of the i30s in the family have the genuine kit (as did Crystal) and they all work faultlessly. In fact, I have had conversations with people where they thought I was sitting at my desk but I was actually on BT doing 110 (ish) on the highway.
I have seen one where they installed the microphone on the windscreen back to front (though it wasn't one of my guys that did it) but even that just made the person in the car sound more distant (no echoes or cutting out).
Be interesting to see what the dealer comes up with.