Heres something you can try.
1) Go to the Audio Category and disable everything in the audio lists. Desktop, mics, everything.
2) Add Audio Input Sources relevant to your Scene. These are devices in Windows sound that are Recording devices, typically your mics, webcam mics, etc. These should be devices that are the default, and in the ready state. Disabled devices and not plugged in won't be used.
3) Do the same for Audio Output devices that you want to capture by adding an Audio Output source. These are devices in Windows sound that are Playback devices. Typically your studio monitors/speakers and headphones. In most cases, you will probably not use these.
4) Other video capture and media devices that can be captured may also be considered like an Elgato/AVermedia/Roxio video capture card, a digital camera audio, VLC Player, etc.
5) For each audio device, use the advanced audio properties and set the monitoring and output appropriately. This controls what you hear on your output devices and if they are to be captured.
Monitoring off = don't hear it on your headphones/speakers
Monitor and Output = hear on headphones/speakers and have the audio captured
Monitor Only mute output = hear on headphone/speakers but do not capture
Example:
Elgato video capture card is set so I can llsten to the gameplay from a gaming console on the headphones and have that audio being captured
Webcam is muted to avoid echoing of what i'm saying in the snowball mic
Blue snowball is a mic for commentary that is being heard on my headphones and being captured
