This happens to me at work every night, the same machine punches and blows air to clear itself and sometimes it seems like super loud like I wasn't expecting it or something even though it does it all night long. I want to say that it's because there's another noise further away I'm honing in on and then I come back.

When I took audio classes, one time we to sit outside with our eyes closed and listened and everyone had to recall what they heard. I heard trucks and low rumbling things. Everyone else heard footsteps, doors opening, a cigarette being lit, etc. I was a truck driver for a few years and naturally hear engines and things over everything else.

You're used to listening to tones, but also noises and things too but may selectively listen and ignore things that are there because that's just the nature of digital sound.

Anyway, I know it's more complex than that as you may not have had the frequencies as accurate with monitors before or something. That's good, I usually listen back on mixes I did in monitors and hear all the noises I couldn't catch and really ruined my faith in monitors. I did however find I could play better with minimal reverbs and things because you can hear that better.