Hello again, After spending some time without my headphones on (which, sort of, prevent me from hearing small sounds around me), I noticed that I could hear the same sound coming out of the speakers (even though the only selected output is the DAC, therefore the headphones) whenever I was launching applications which are dealing with audio (games, voice chat applications, etc.).
Therefore, I think I was wrong assuming it could be gnome-settings-center, because that's all I had been seeing by then, but know it seems it could a broader issue, or, at least, because of other packages. Sorry for the inconvenience, JB
