What is the knocking in Act 2 Scene 2 in Macbeth?

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teachersyl eNotes educator| Certified Educator

At the end of the scene, Macduff and his companions are arriving at the castle. They apparently had been told by Duncan to come early-- indeed, earlier than Macbeth had expected them. The last line of the scene has Macbeth shouting, "Wake Duncan with thy knocking! I would thou could'st." The exasperated plea is similar to the cliche that something is so loud, it could wake the dead. Macbeth immediately follows up with a statement of guilt. He regrets what he has done, and the guilt will subsequently consume him.