I too have the problem with the "System" and "System Interrupt" showing high CPU, and my fan going nuts every now and then. Mine problem will come on if I am using the computer for some time, and then if I shut the computer down, sometimes it will go away for a day or so. Mine really doesn't have a pattern, so maybe there is some maintenance going on in the background as I think Megatronium may have mentioned in your 1st thread. I didn't have this problem until the 9/9 updates, however.
Anyway, I was trying to figure what was going on so I right clicked on "system" from task manager, and went to properties which brought me to a Ntoskrnl.exe application which stands for the NT Operating System Kernal (which I see listed in your resource monitor I believe).
I started searching this file which led me to this site:
http://forum.sysinternals.com/need-help-with-ntoskrnl-thread-causing-high-cpu_topic29289_page1.html
One of the early posters, MagicAndre1981, mentions using Windows Performance Tools, which lists the sites for download, and then running a command to gather data to isolate the problem (at least for Ntoskrnl.exe). For a lot of the participants in the threads, they had out of date or corrupted drivers.
I haven't had time to try this out yet, but perhaps it may help you??
