The interpretation that could be made about 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 overall themes of guilt and madness in the play as Lady Macbeth is deeply involved in the plot to murder King Duncan, and the reference to the owl, often seen as an omen of death, reinforces her growing unease and the psychological turmoil that follows their heinous act. The owl's shriek symbolizes the foreboding nature of their actions, indicating a shift in her mental state as the gravity of their plan weighs heavily upon her.