knocking

noun

Pronunciation: /ˈnɑkɪŋ/ / /ˈnɒkɪŋ/

An act in which something is knocked on, or the sound thus produced
“These strange openings and closings and knockings were warnings and reminders from the spirits who attend the dying.”
“There was no response to continued knockings.”
A repetitive ping, knock, or similar sound coming from an engine in which there are repeated uncontrolled explosions in the combustion chamber.
“Sir―I was greatly interested in a short article in The Motor Cycle on the subject of engine knocking.”
“Knocking can also occur at high speed, but that may go undetected by the driver.”