Ok so there is a slight problem on the Logitech G610 keyboard: when the backlight is on, a subtle high-frequency squeak comes out of the keyboard which is pretty annoying, especially if you have a good ear like me. And this squeak occurs when the backlight power is less than 100%. Here are the steps how to fix this:

1) Turn the backlight on full power
2) Open the program Logitech Gaming Software, then go to Lightning Settings
3) Select the level of illumination in Stock
4) Click on the color square on the Effect Selection box.

Here’s the screenshot: