Altan's "Donal Agus Morag" was playing, but the Now Playing page says it was:
Song: Celtic Odyssey
Album: Runaway Sunday
From what I could find, that album doesn't actually have a song called "Celtic Odyssey" on it, though I was relying on Internet sources and may have incorrect information on the contents of the album.
Nevertheless, the song was definitely "Donal Agus Morag," which I believe is from Altan's Harvest Storm.