SRD:Thundering

Thundering: A thundering weapon creates a cacophonous roar like thunder upon striking a successful critical hit. The sonic energy does not harm the wielder. A thundering weapon deals an extra 1d8 points of sonic damage on a successful critical hit. If the weapon’s critical multiplier is x3, add an extra 2d8 points of sonic damage instead, and if the multiplier is x4, add an extra 3d8 points of sonic damage. Bows, crossbows, and slings so crafted bestow the sonic energy upon their ammunition. Subjects dealt a critical hit by a thundering weapon must make a DC 14 Fortitude save or be deafened permanently.

Faint necromancy; CL 5th; Craft Magical Arms and Armor, blindness/deafness; Price +1 bonus.