が揺れる音

the sound of something shaking

→ が
phrase Rare #39,804
the sound of something shaking A noun phrase meaning “the sound of [something] shaking.” The noun before が is the thing that is shaking; depending on context, “rattling” or “swaying” may be a more natural English translation.
JA: 窓が揺れる音が聞こえた。
EN: I heard the sound of the window rattling.

の中のビー玉が揺れる音

(The sound of marbles rattling inside a bottle)

— 万引き家族 (2018)

校舎が揺れる音

(The sound of the school building shaking)

— すずめの戸締まり (2022)

部屋が揺れる音

(The sound of the room shaking)

— 天気の子 (2019)

風鈴が揺れる音

(The sound of a wind chime swaying)

— 万引き家族 (2018)