How to get rid of the noise in speakers produced by mouse use (graphics/GPU use)?

The solution for these USB-powered speakers is to power them by an other USB power source than the computer itself. The 3,5 jack is still connected to the computer, but the USB power caple of the speaker set I've plugged into an external USB power source that's not related to the desktop PC. Now the GPU/CPU humming sounds aren't hearable anymore.

This is what made me to come to this solution: After some testing I found out that the sound doesn't appear with headphones connected or with a speaker set that has its own power supply instead of power supply by USB. However it did at some occasions (but not always reproducable) appear when using the built-in audio of the monitor screen that is connected via HDMI.