GURPSよろず

see p. B85
　When 「音を立てない」 occurs in fiction, it’s typically the result of a physiological adaptation, like a cat’s padded feet.
However, stealthy supers and robots sometimes have an active capacity to dampen sound or “project” silence.

■代替案（Alternatives）
To create a zone of silence, use 「知覚されにくい」 (Hearing) (p. 64). 「範囲に効果」 isn’t suitable for the 「音を立てない」 advantage.

■追加特別増強（New Special Enhancement）
Dynamic:
　Your ability actively cancels out the sounds you make when you move, or helps them blend in with ambient noise. You enjoy your full 忍び bonus (+2 per level) when moving. +40%.

■パワーアップ（Powering Up）
　「音を立てない」 most often belongs to an elemental or psionic Sound/Vibration power. It suits body-control powers, too --especially the chi-based powers attributed to legendary ninja. It would also be logical for an animal-control or shapeshifting power that lets the user borrow the features of stealthy predators. 才能 adds a further bonus to 忍び skill rolls to avoid being heard.