My hardware is a custom AMD 6100 CPU & Asus M5A97 Pro Mobo with Win8 and a 2002 Apple Pro Keyboard.
It's incredibly annoying, especially when typing. (Just then the Windows button triggered when I pressed L and locked the screen.)
Unplugging the keyboard helped, but it still occurred, and then I don't have a keyboard.
Also, it seems to start slowly after about 2 hours of use, speed up to almost twice a second every 10 seconds and then slows again.