As mentioned in the comments, this is a harmless warning that informs you that a package has been installed or removed directly using the
rpm command instead of
yum. The difference is that
yum is smarter in automatically resolving dependencies, and it is the default way of keeping the package-management DB on your system up-to-date (hence the warning).
See Execution of yum leads to "Warning: RPMDB altered outside of yum." for an official explanation of the message on the Red Hat Customer Portal.
To get rid of the warning, run:
# yum history new
See also yum or rpm, which contains further explanations and links to Red Hat documentation about both Yum and RPM.