Vista - High CPU usage in Performance and Resource Monitor?

I'm posting here because we are talking about performance and resource monitor.

As I have noticed before, my machine last night started being quite audible, sounding really busy. When I looked in task manager and performance and resource monitor I noticed that my cpu usage was running between 55% to 70% without Firefox or IE8 being loaded. This may be normal, yet my question is why could I not see that usage in either monitors? Something under system (kernel......?) was showing the biggest usage of about 20% but the rest of the list showed either 0% or perhaps a few kept fluctuating between 1% to 2% but there was nothing I could see that added up to what I was being told the usage was. My memory usage at that time was about 23% to 25%, disk usage 1%. So, what kept my machine so busy? This morning all is back to normal cpu around 3%, memory about 33%.

I would first check to see what programs are scheduled to perform scans around that time. Depending on the settings (daily, weekly, etc) it may take a while for it to recur.

When you open up Task Manager, go to the Processes tab.
Make sure that you click on the button in the lower left that says "Show processes from all users:
Then click on the View menu item, then on the Select columns menu item.
Place checkmarks in the I/O Reads and I/O Other boxes and click OK to exit the dialog.
Then expand the Task Manager window so that you can read the columns (you can double click on a column header to sort by that column).

Then wait for it to happen again - and check for the highest numbers in each of the columns. Let us know what you find and we can work from there.