Normally unit want to avoid audit, most of time without any reason.Give the information to the department. Invite them to aidut your records. If there is any short payment of duty, pay it promptly. If they raise any frivolous objection, contest it.
Normally people fear audit for harassment. I will tell you a "trick" to avoid harassment in all checks;
-Give all documents to the officers, whatever you have. After giving all the documents etc,, and a room for them to sit- leave that room for auditor to audit in peace. Never request them to finish audit soon. Let them take their time. Preapare a list of documents submitted to audit, and get it signed by the auditors.
-Refuse to answer any questoin at the time of audit or in a hurry. Say that they can check the records fully and raise objection- the unit can reply only after checking the facts and consulting their consultants.
Just try it once, you will see the difference.