What is the meaning of knocking?

noun

• The sound of knocking (as on a door or in an engine or bearing. )
  • usage: "the knocking grew louder"
  • synonyms: knock

verb

• (v.) ()
  • synonyms: knock, strike hard
• Rap with the knuckles.
  • usage: "knock on the door"
  • synonyms: knock
• Knock against with force or violence.
  • usage: "My car bumped into the tree"
  • synonyms: bump, knock
• Make light, repeated taps on a surface.
  • usage: "he was tapping his fingers on the table impatiently"
  • synonyms: tap, rap, knock, pink
• Sound like a car engine that is firing too early.
  • usage: "the car pinged when I put in low-octane gasoline"; "The car pinked when the ignition was too far retarded"
  • synonyms: pink, ping, knock
• Find fault with; express criticism of; point out real or perceived flaws.
  • usage: "The paper criticized the new movie"; "Don't knock the food-it's free"
  • synonyms: knock, criticize, criticise, pick apart