knocking

verb

1. (form-of, gerund, participle, present)present participle and gerund of knock

noun

1. 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.”

   “Recorded live to CD with new instrumentation--artillery shells, tuned suspension cables, boxes filled with springs--and deemphasized guitar parts, it's a beautiful collection of echoes and whispers, drones and knockings, with a gently swelling sense of the sinister.”

2. 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.”