Your songs are loud enough to deafen creatures damaged by their effects.
You can modify a song to deafen a creature damaged by the song. When a creature takes damage from this song, it becomes deafened for a number of rounds equal to the original level of the song. If the song allows a saving throw, a successful save negates the deafening effect. If the song does not allow a save, the target can make a Fortitude save to negate the deafening effect. If the song effect also causes the creature to become deafened, the duration of this metasong effect is added to the duration of the song. Songs that do not inflict damage do not benefit from this feat.
MP Increase: +2 (a thundering song costs 2 additional MP more than the actual MP cost of the song.) In addition, the perform check DC increases by +2.