I wish I could answer to the other answers here, to make this a bit more conversational. I couldn't find the option to do so, if it exists I don't know how to use it.
Anyways, since this question has now being commented, I figured I'd update it with the latest developments on my issue.
After asking the question, I tried other things such as:
- Moving myself away or facing different orientations. No proper fix to the issue, but it did prove to affect the intensity of the noise. When I faced my window, the noise seemed to be in its loudest (hold on to this last information for a while);
- Changing cables. While changing one AUX cable with poor EMI insulation used in my setup to a better one helped mitigating the problem, it didn't properly solve it;
- Enveloping the Audiobox with in foil. I don't mean to wrap it with tin foil, but to create a housing or a cage to it. This was by far the best option I took, but never fully solved the problem, again. Maybe with a bit more patience to apply the foil to a shoe box and then place the Audiobox inside it, the results could be better, but who wants to have to do this anyways?
It just so happened that I moved during this period and now, in my new place, that also happens to be a new construction, the Audiobox works as smooth as possible. NOT A SINGLE NOISE! Well, there is noise, there always is, but now it's within the boundaries of accepted white noise. You can't even hear it when listening to the recording.
So what changed? Why did I have noise on my old place, but the same Audiobox performs very well on my new place?
I can't really point to the exact culprit, but I have my guesses. Earlier I referred to a window, well that window faced a school and an electric train track. It could've been that some equipment in either of these places was generating EMI signals, which were being captured by my bass guitar and my setup cables. In the end, the bass guitar and the cables do behave as antennas.
The other option is that a device in my own old building, from my apartment or not, was injecting noise in the circuit, and this noise made it's way to the Audiobox. Potentially could've been solved by trying to use another electric circuit in the house or be checking/fixing the circuit grounding. Well, I'll never know, since I didn't try it.
What was interesting is that in the meantime I did find a video from Samurai Guitarist where he faced similar noise issues, when he moved to a new place. In his case, the noise could be heard from the guitar speaker itself. He later found out that one of the power transformers from his utility on the neighborhood was faulty. Most likely it was due to a faulty shielding/grounding of the transformer. He was lucky enough that the utility fixed the transformer and his issue.
Check his video here: or search for "Solving Another Mysterious House Noise" by samuraiguitarist.
Unfortunately there is no easy or direct solution to the problem, but at least this gives us some ideas on what could be the problem and what we can do about it.