I've got a kvoop process that use 100% cpu and slow down the use of the web interface. We sometimes have a popup telling us that the server is too busy and it asks us if we want to cancel our request. I could not find what was the use of this process. When the server begin to slow down, I kill the process with a kill -15 <pid>.
I'm sure it's not a good way to solve this problem.
We actually use Zimbra 4.5.0_GA_612.RHEL4 on a Redhat ES4.4 cluster.