Thanks for your reply.
It worked without rear cover, but at this moment I can't turn on my smartphone.
It's probably motherboard failure, but I will measure also battery voltage.
@Edit Probably discharged battery. It turned itself.
So it has just turned on. I guess It will happen again. Then I...
Yes, the same. It's even when I enter to Menu application and I hear for approx. 3 seconds this hum. Even I click on Calculator and I hear some kind of hum. But it is hearable all time when I listen to music.
I haven't rooted Android.