In the beginning sequence of Game of Thrones S06E06 we see Bran's visions, and in them the Mad King cries "burn them all!" many times. But when Myra stops and touches Bran's face, during his vision of him falling from the tower, we hear somebody calmly say "burn them", immediately followed by the Mad King's shout. Can somebody recognise the voice?
Here's that sound fragment.
First I thought it was Jaime, but I rewatched moments when he repeated the Mad King's words previously in the series, and this doesn't sound like those.