VMs are very slow to respond after a period of inactivity

hello,

i heave three nearly identical multi core hosts running centos 4.4 and vmware server build 29996.

common to all systems is that the VMs that have not seen any usage for a while are very slow to respond (these are dev machines which receive little traffic)

i have checked the "fit all virtual machine memory into host ram" setting. nevertheless, after a period of inactivity (hours/days), accessing the virtual machine feels as  slow as when you resume your laptop from standby with many apps open.

i'm wondering if someone else have the same problem?

cheers,

-paul