Rob,

Do you have SQL Sentry or SQL Monitor in place? Your post regarding backups jogged my memory of a simlar situation with one of my production environments where processing a particular cube was causing havoc with I/O and CPU to my other databases. Depending on what kind of event processing is taking place TempDB residing with Primary could definitly be the culprit as could file growth on your production systems if it is set to autogrow etc.

Teal Canady