When keyboard lights (further KBL) are off - no pitch noise, when KBL are on - there's a bothersome pitch noise. Also I've noticed the following: when I switch KBL on and pitch noise appears, I press functional volume buttons (Fn + F11/F12) and the pitch noise dissappears for some time.
The next thing I've noticed is that there's no pitch noise when I boot to BIOS settings, but KBL are on!
I use Ubuntu 14.04 LTS, kernel 3.13.0-32-generic. Tried to update kernel to 3.16.0 and 3.16.1, but no results.