Knocking has 3 different meanings across 1 category:
Noun
the sound of knocking (as on a door or in an engine or bearing)
"the knocking grew louder"
An act in which something is knocked on, or the sound thus produced
"The rhythmic knocking from upstairs woke me just before dawn."
present participle of knock
"The knocking on the door kept me awake all night as I tried to fall asleep."