I'll try to answer some of your questions but it is hard to determine where the noise is coming from if we can't hear it. Maybe you could post a song with the noise so we can try to determine where it is coming from. Also putting you system's data in your byline would help us.

1- the free Audacity and its plug-ins can do many things to a wav or MP3 including taking out noise. https://www.audacityteam.org/

2-Maybe but we would have to hear it. However it shouldn't be adding noise.

3-yes If the noise is not generated by your computer.

4-If the mic and fan are both on when you are recording then that could cause noise.

Have you tried to record anything other then BiaB? Try recording a youtube audio. Does it have noise? Doing this may determine where the noise is being generated, either by your computer and sound card or your recording.

A couple of last thoughts do you have a cell phone that is on near your computer or keyboards? We have had problems here with musicians having a live phone generating noise while recording and listening. Is your computer very close to your modem or router? That can generate noise also.

I hope this helps and good luck.

Me, it's not about how many times you fail, it's about how many times you get back up.
Cop, that's not how field sobriety tests work.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware