The most accurate interpretation of the owl that Lady Macbeth claims to hear is:
Lady Macbeth is beginning to lose her sanity and only thinks she hears an owl shrieking.
This interpretation aligns with the themes of guilt and mental unraveling that both she and Macbeth experience following their violent actions. The owl's shriek, often associated with death, foreshadows the tragic events to come and symbolizes the disturbance of natural order caused by their ambition and subsequent crimes.