Acabamos de encontrar uma solução para isso:
First, Close your browser or any other programs that are using your microphone.
Open Regedit Navigate to [HKEY_CURRENT_USER\Software\Google\Google Talk Plugin]
In this section it should have a string value named "audio-flags" with a value of 3
Change this value to one so it reads like "audio-flags"="1" or as seen below in the picture.
Once you've done all this you can open your browser and launch googletalk/hangouts. I've noticed that if I ever open the hangouts settings tab to adjust any settings it does reset this setting. So be prepared to do it over again if you do that (and subsequently reset your browser).
Confirmei que isso funciona.