CPU overload issue with several sites on dedicated server

I have about 10 WP sites running on a dedicated server. I never had an issue with any of them until I migrated from a VPS to a dedicated server.

server is centos 4, running php 5.3

I get the following under apache status, transmitted 100s of times for each of the sites:

xxx.xxx.xxx.xxx GET /wordpress/wp-content/themes/index.php HTTP/1.1

the ip address associated with the request (xxx area) is the main IP address of the server. It appears as if somehow it is generating its own traffic loop.

3 of the sites get only about 10-15 visits a day, and are only comprised of 3 pages and 1 post, so I know its not traffic that is driving the issue.

I have tried optimizing the database, that does nothing. I have tried turning off all plugins, that does nothing.

Within 1 minute of unsuspending the account, server load will go to > 100 and slow everything to a crawl.

I have checked the sites extensively for hacking/virus, including searching in the database to see if there was an injection, there is nothing there. I see that in the past others have had this issue but have never seen a solution as to why WP all a sudden is going haywire.

I have other WP sites on the same server which have no issues at all and are working fine. The sites in question run fine when unsuspended (no errors generated), until they overload the server and I have to shut them down.