山田さんの声が後ろから降ってきたのだ。
山田's voice came falling from behind.
What is the nuance implied by 降る here?
- 後ろから山田さんの声がしたのだ。
- 後ろから山田さんの声が聞こえたのだ。
- 後ろから山田さんの声が降ってきたのだ。
Putting aside the fact that the sentence 3 is uncommon and a bit literary, the semantic nuance of the sentence 3, if any, is that the voice came unexpectedly and suddenly.
A figurative expression "空から降ってきたような話" means "sudden and unexpected offer". There's an idiomatic phrase 降って湧く which means "(something) happens suddenly and unexpectedly".