Have you changed the settings in any way from the default?

Even with my settings on High, there is barely any noticeable effect on my system and yours has a much faster cpu.

‘Even when you are installing’ what?

If you have settings set to High it will scan all newly created/modified files. What are your settings.

http://img.photobucket.com/albums/v325/for-dwr/scanner-adv.jpg