The feedback issue is typically a software related problem.

1.  Goto Control panel, then to Sound and Audio Devices.

2.  Go to Voice tab, click on the volume button.  Once the Volume options are open, click the checkbox for Mute on Stereo Mix.  If Stereo Mix is not available, go to options (circled in bottom pic) select the properties button and it will have options for hidden devices.  In which case check Stereo mix, click the OK button, then Mute it as already stated.

3.  Close out all sound windows and retest.