The auditing of a company's financial records by independent examiners on a regular basis is necessary to prevent "cooking the books", and thus to keep the company honest. We don't normally think of auditors as listening, since looking at and adding up numbers is their basic line of work, but auditors do have to listen to people's explanations, and perhaps that's the historical link. Hearing is more obviously part of another meaning of audit, the kind that college students do when they sit in on a class without taking exams or receiving an official grade.