windows 7 - ~100% CPU Usage with little CPU Process utilization

Fresh install Windows 7 on single core desktop. Windows Task Manager:

• Performance Tab: spikes to ~100% CPU usage for long periods (30+ seconds)


• Processes Tab: sum of CPU column is < 4%

Windows Update -> Install Updates seems to cause trigger this event. Is there a simple / clever technique to determine if there are any other services that are significantly consuming CPU usage?