Disable Search Indexing in options. It uses a buggy piece of garbage called Akonadi in the background and was causing one core of my CPU to stay at 100% for no reason.
I'd love it if the KDE devs made Baloo and Akonadi optional. Their insistence on including them reminds me of Micro$oft's insistence on bundling Internet Explorer and integrating it into the OS shell in Windows 98.