Source: Epic Level Handbook
Your rage attacks can cause thunderous roars that can deafen opponents.
Prerequisite: Str 25, rage 5/day
Benefit: Any weapon you wield while in a rage is treated as a thundering weapon (see the DUNGEON MASTER'S Guide). The DC of the Fortitude save to resist deafness is equal to 10 + 1/2 your level. This ability does not stack with similar abilities (for instance, if the weapon is already a thundering weapon).