On Kubuntu 12.10 I can see with the KDE System Monitor Plasmoid that the CPU usage is fluctuating between 60% - 90% on both cores. As soon as I open top it goes down to 3% - 10%. I thought that the issue is that I'm 'doing nothing' while looking at top, so I closed top (just pressed q) and still did nothing with the keyboard nor mouse. However the CPU usage jumps back up to where it was. What might be smart enough to calm down while top is running?
If you do something while top is closed, like type slowly in kedit/gedit and the cpu usage goes down then this supports the theory that some on-idle process is running and running top is not counted as being idle. While doing nothing while top is closed is counted as being idle, so the on-idle process roars to life.
What does the following command reveal?