What causes nightly email on "yum" available update?

[B Wooster]

In FC5, every night, I get an email (to root), with subject:
Subject: Updates available for <machine name>
===
=== yum reports available updates:
===

...

Looks like output from "yum check-update"

I need to disable that - don't really need to know every day what is
new, how do I disable this?

There is certainly no check-update job in /etc/cron.daily (there is a
yum.cron there, but that is for automatically applying updates, and
the default is off, so that job is certainly not running).