How to solve the Win7 computer's shrill sound

1, encountered this situation is after dinner, so when the notebook when the difference sounded really scared me a big jump, not only that, even the neighbors came out to ask what is the situation, this shows that the situation is compared to let me crazy.

2, because my notebook has been in the case of sharp abnormal, so I first the volume of the notebook to the minimum or directly click on the speaker set to mute, so that the sharp screaming to stop.

3, but we have to use the notebook normally can not keep the notebook in a quiet state. The next small series for you to introduce a permanent solution. First click on the mouse on the bottom right side of the horn symbol, as shown in the picture:

4, then will pop up a small window, continue to click on the small window to raise the speaker symbol, as shown in the picture:

5, the next pop-up "Speaker Properties" dialog box, in the dialog box to select the above "level" option, as shown in the figure:

6, in the "Level" interface to set the microphone to mute, as shown in the figure:

7, then try to turn the speaker's voice slowly to the maximum, there is no harsh howling sound!