First I'd check to make sure it is the initrd. In /etc/grub.conf you should see the different lines for the kernels. If you are using an initrd you'll see something like this:
title Red Hat Enterprise Linux Server (2.6.18-274.3.1.el5)
kernel /vmlinuz-2.6.18-274.3.1.el5 ro root=/dev/VolGroup00/LogVol00 rhgb quiet
Make sure that the initrd matches the version of the kernel - IF it is being used. If the initrd is different from the vmlinuz version or if you see the initrd on other kernels installed it probably means you need to update it. I'd contact redhat support for assistance updating the initrd. Modifying the initrd can render your system unbootable - so it is highly recommended to have assistance from them.