I have a Windows 2008 R2(fully patched) machine with SQL 2008(patched). During random parts of the day the LAN usage will spike to 100% for just a moment, drop down to almost nothing for about 10 seconds then spike again. It reports this in Windows but not in vCenter. It repeats this for various periods of the day. Rebooting this server clears it up for a while. It does this with SQL turned off as well. No files are shared out on it. Has anyone seen this. We're running ESXi 5.1.
Did you check TCP connections on guest OS?
Which type of virtual NIC is using by you on them? VMXNET or E1000?
Try to install latest VMware Tools. IT's available at this path: Index of /45848/tools