Below is the original issue originally submitted as a problem to the Windows category.
This is a strange issue, but when I start a VM on my Windows host, if the Audio is turned on and not set to the null device, it will immediately turn on the microphone. Using my USB headset, you will immediately hear a hissing noise from turning the microphone on. Muting the microphone through the headset does no good, although it does keep me from hearing myself. As far as Windows is concerned, the application (VirtualBox) is requesting access to the microphone. The same hiss comes when you go into sound settings in Windows and click the record tab, where it enables the microphone. It would seem the right solution is to have a setting in VirtualBox that allows you to disable microphone. So to be clear, the issue isn't that the microphone produces a hissing noise when enabled, but rather that VirtualBox enables the microphone immediately upon starting a VM because the guest may want to use it. Since Windows has no way to know if a guest VM application needs access to the microphone, this is understandable, but there should be a way to disable the microphone entirely with a VM and not by way of disabling it in Windows.