Overiding Hiss Just Started While Recording

I'm afraid that even if you could undo the 'update' that M$ has foisted on you, it wouldn't necessarily reset the audio system. You may need to find somebody local to you who can help.

As for how they can do this to you, the answer is very simple; it's because they can. They are a global version of what we in the UK call the 'Nanny State'; they think they know best about what's right for you and are going to force you down a particular route with your computer, regardless of what you actually want or need. And, they've had run-ins with the RIAA over things like streaming music copyright, so anything to do with audio they regard with deep suspicion, because apparently we're all breaking the law pretty much whenever we do anything with it at all, however legitimately. So they tend to make things as difficult as they possibly can.

For people using a PC regularly for audio recording, there's a much easier and more effective solution - you use an external USB sound interface with an ASIO driver. This effectively bypasses the operating system, and you have full and direct control over it as a recording device. Even this isn't guaranteed to be completely trouble-free, but it's way better than using an internal sound device, any day of the week. There are other advantages too; the sound quality is invariably better, and the device noise levels are inherently lower because it's situated outside the noisier electrical environment of your computer.