RHEL Warning: RPMDB altered outside of yum

When I try to update my server using the yum command I've been seeing the following error / warning message:

yum install aide
Loaded plugins: rhnplugin
Setting up Install Process
Resolving Dependencies
--> Running transaction check
---> Package aide.x86_64 0:0.14-3.el6 will be installed
--> Finished Dependency Resolution
Dependencies Resolved
=============================================================================================================================================================================================
 Package                                Arch                                     Version                                        Repository                                              Size
=============================================================================================================================================================================================
Installing:
 aide                                   x86_64                                   0.14-3.el6                                     rhel-x86_64-server-6                                   123 k
Transaction Summary
=============================================================================================================================================================================================
Install       1 Package(s)
Total download size: 123 k
Installed size: 0
Is this ok [y/N]:
Downloading Packages:
aide-0.14-3.el6.x86_64.rpm                                                                                                                                            | 123 kB     00:00
Running rpm_check_debug
Running Transaction Test
Transaction Test Succeeded
Running Transaction
Warning: RPMDB altered outside of yum.
  Installing : aide-0.14-3.el6.x86_64                                                                                                                                                    1/1
Installed:
  aide.x86_64 0:0.14-3.el6

How do I fix this problem?

The message means you either used rpm command to install / remove package or other application made changes to the rpm database without using Yum API. This is just warning. To avoid this warning I recommend only using yum command or API to install, query, delete packages. To remove warning simply run
# yum clean all