Additional note: Whenever you have the crank gun out, this same audio bug happens. Even a tiny hop up the stairs or a fall down from a table results in the maximum volume impact sound, as if your character had just fallen from a great height.
For a moment I thought that this might be a deliberate decision to emphasize the heaviness of the crank gun, but no, the comparably heavy drakefire gun doesn’t have this audio issue.
Only spear & shield, masterwork pistol, and crank gun suffer from unvarying falling noises. Every other weapon in the game uses different volumes for impact sounds depending on the height you fall from.