UPDATE: Still waiting for some advices. I tried to disable almost all devices from BIOS that I could (WLAN, Bluetooth ...), the sound remained. Then I booted Linux distribution from CD, still the sound remained. Then I launched Memtest86, there were no sound during the test, so I thought that CPU might be the problem. I launched ''Intel Processor Diagnostic Tool'' and something changed, during the test high pitched noise was gone, there was very quiet constant buzzing instead. When all tests were passed (without any problem) the high pitched noise appeared again. So I'm pretty sure CPU is making that noise. During the test CPU usage according to Task Manager was 100%. I attached test results from Intel Processor Diagnostic Tool.
So is there something that could be done to reduce that noise, maybe change CPU frequency a bit?
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