So a while back on this list (I can’t find it) I posted that periodically, I would find the “System” process in task manager using “13%” CPU for a period of time (i.e. 12.5%, or 100% of one core) … (the CPU “bar” would show up as red, and not green.)
Eventually I got fed up with it and ran some “etwrecord” script while the issue was occurring. After pouring over the data, I eventually found a section that said seemed to say somebody was trying to open c:\windows\system32\drivers\etc\lmhosts over 32,000 times.
This led me (via a very helpful forum post [1]) to the following KB article:
http://support.microsoft.com/kb/955860
Which says “High CPU usage occurs for six seconds on a Windows Server 2003-based computer that has multiple network adapters”. It says it only applies to Server 2003 but I was definitely having the issue as well on Windows 7; disabling lmhosts lookup completely solved the problem.
[1]
http://forum.sysinternals.com/windows-7-system-using-high-cpu-intermittently_topic20786.html