Ghost backup process (still runs)

This is really strange. I configured a backup a few months ago to back up my data drive, but then deleted it (it doesn't show up in my list of backups on my home page). But every night it still does a differential backup, and I don't see any way to stop it. If I delete it on the file system, it creates a new full backup and starts doing differential backups again. How do I delete a backup job that isn't even there anymore? Is there something on the file system or in the registry that I need to nuke?

Sam