What or Who is taking SQL Server backups
The reason why you don't is because an agent is taking the backup. Look at Windows Services for something with "backup" in it's name like NetBackup or Tivoli (TDP, TSM) the service would be running using System account. The virtual device is a temporary mount point. The backup agent is sending it to an external storage then should put it to tape. Agent don't always have a GUI and a shortcut in the Start Menu. You can look also in the installed programs for a hint.