I realize this is an old post, but ran across it working on a SQL Audit issue myself
For any future reference:
Look for the Server-Level Audit Action Group - AUDIT_CHANGE_GROUP
This event is raised whenever any audit is created, modified or deleted. This event is raised whenever any audit specification is created, modified, or deleted. Any change to an audit is audited in that audit.
MCITP - Database Administrator (SQL 2008)
MCSE: Data Platform (SQL 2012)