Most likely you are seeing one of the effects of the embedded NIC driver issue.http://www.intel.com/support/motherboards/server/sb/CS-031086.htm?wapkw=(high+cpu)
These were several NIC drivers released as well as a BIOS option switch to address issues such as your describing (kind of)
I would recommend:
1) Updating to the newest code stack posted on the board support site.
2) Boot into BIOS set-up and press F9 to reset the defaults. (make sure you know any settings you have changed from default before you do this so that they can be reset)
3) Restore your customer BIOS settings and F10 exit
4) load the newest NIC drivers
Issues should all go away.