There's a lot wrong with the custom sounds on the latest versions of Forge. Regardless of the distance to the otter, the volume of its whistling is the same. It's maddening. With vanilla mobs this problem does not exist.

Modpack - https://www.curseforge.com/minecraft/modpacks/play-as-dragon
Forge - 1.40.73
Mod - crittersandcompanions-1.18.2-1.0.1