I have set up a job to backup a database daily. I was surprised recently to find that backups are being done every 2 hours for the same database. These are listed in event viewer (source: MSSQLSERVER, user: N/A) along with the expected backups. They are also listed in SQL Server logs (Source: BACKUP). However there is no associated SQL Server Agent job and there are no maintenance plans. Queries against various system views turn up nothing but the expected job. I'm using SQL Server Manager as sa.
How do I find and modify this backup?