を叩く音

sound of knocking

→ を
phrase Rare #36,760
sound of knocking A phrase pattern meaning the sound of knocking or tapping on the object marked by を. The object can be a door, window, pan, or someone’s back.
JA: 窓を叩く音が聞こえます。
EN: I can hear the sound of someone knocking on the window.

背中を叩く音

(Sound of patting someone on the back)

— 万引き家族 (2018)

フライパンを叩く音

(Sound of banging on a frying pan)

— 紅の豚 (1992)

を叩く音

(Knocking on the window.)

— 万引き家族 (2018)