knock

/nɑk/

the sound of knocking (as on a door or in an engine or bearing)

中文释义：敲击声；敲门声

I heard a loud knock at the door just after midnight.

刚过午夜，我听到一声响亮的敲门声。

The engine made a strange knocking sound when I accelerated.

我加速时发动机发出奇怪的敲击声。