CPU Overload

Hi

I have two esxi 5.1 Host that manage with vCenter

i saw odd thing in 2 last weeks on CPU Performance

both hosts had jump on CPU Usage performance Graph two times

and it happend exactly in same time for 3 or 4 hours!!!!

if these help:

-i never used "Vmotion" or "HA" or "DRS"

-i have almost 120 VM on both host and i use RAID-10 storages and intel E5 CPUs

-CPU is NOT share on VMs

-i didn't change anything in this weeks just add & remove & Upgarde VMs

-The health status in one host is normall and in another one i have a warning for 6 months: chassis->"system chassis 1 chassis Intru:General chassis intrusion-Assert" but i never saw any problem this 6 months

any idea?

thanks alot