knocking(n = noun.event) knock - the sound of knocking (as on a door or in an engine or bearing); "the knocking grew louder"
is a kind of sound
Derived forms verb knock₂, verb knock₅

   A beating; a rap; a series of raps. [1913 Webster]
"The . . . repeated knockings of the head upon the ground by the Chinese worshiper." [1913 Webster]