Control Panel - Sound - Playback tab - Speakers - Right click Properties - Level - Just turn the microphone sound to 0.

Extended reading

Double-click on the volume icon in the lower right corner of your computer desktop.

Click on Options in the Volume screen.

Click on the Properties option.

Under the Playback screen find Microphone Volume and check the box.

Remember it has to be under the playback page because there is also a microphone volume under the recording page.

Now double-click on the volume icon in the bottom right corner of your computer desktop again and click on the Advanced option under Microphone Volume.