...unmute the Mic. This produces instant noise but doesn't record my voice...
So your mic is noisy. The question is, "Why?"
Is the room actually that noisy? Be brutally honest: your ears to a fantastic job of cleaning it up and ignoring the background, while the machine does not.
What about electrical noise that gets into the wiring for the mic? Things like a refrigerator, air conditioner, light dimmer, or even the computer itself.
It might be good to post a recording of that noise. Different problems sound different. A logfile wouldn't hurt too, from the same session that produced that recording.
Help -> Log Files -> Upload...
Copy/paste the URL that it gives you, both here and into the automated analyzer that you can get to from my signature.