I just pulled out Winter Turning, there is mention of a someone playing a stringed instrument in Possibility.

The closest I've found to flutes is "a conch shell fanfare" in Darkstalker at the SeaWing party. The musicians at the party were playing "the queen's favorite instruments" but did not specify further than that.

I feel like a flute isn't too much of a stretch if they use conch shell horns.