Interesting....
Someone is doing Black Metal vocals

Reminds of what I used to do along time ago when I first got a cellphone with the ability to record...
Press Record and sing De mysteriis dom sathanas (by Mayhem)
Also reminded me, me Trying to Prove that I RECORDED GHOST SOUNDS WITH IT! Hahahahahahahahahahahaha
Seriously, I used to have sooo much fun back then (scaring my friends etc - But I NEVER took it to the internet)

Anyway, If you are doing that now I am not blaming you kid!
Now what it could be, apart from you doing it ?
Let's assume that it's real!!
Have you ever tried recording with a cellphone your class ? (while you are having lessons ?)
You will be like "What the ? Are we so noisy ???!!!
(the waveform will be huge, even when only 2 people are talking/whispering in a pretty big room)
Or try recording your room (when you think everything is silent) various weird sounds will be recorded, the "accelerating" car sound you didnot expect to be "captured" within the recording will sound like a growling monster, your breath (if you are close to the cellphone) etc etc
(OUR Ears are Adapted to such sounds...
It's like listening to loud music... after a while the music isnot that loud, your ears 'adapted' to the volume... But you look at the cd player, see the "18/20 volume" and say eh ?!
You are at the cinema and watching the film... The film just started a car exploded (in the movie) and you go like MY EAAAAAAARSSSSS... After 30 minutes everything is fine explosions don't "hurt" your ears any more!
Thus the microphone is never adapted and cannot be fooled!!! )
That was recorded at your school a place full of noisy people (it is veryyy noisy believe me), even if you didnot expect such noises to be captured (because you thought you were to a silent room) such noises are to be captured (in most cases).
But that is the problem!!!
In this clip we only hear the voice... no ambience!! The "Hiss" level is low as well
(Even if you recorded it through your cellphone (ADD HISS) and then to your pc (ADD MORE HISS (+the sounds of your room) !!! ))
You must have edited the waveform (added some Db, and removed hiss, etc). Didn't you !?
The sound of the voice is way too loud and clear!
Was it like that or you brought it up ? (through editing)
Even the clearest recordings of so-called "Ghost Sounds" arenot that clear.
So if that is 100% original, then it must be Satan who got bored of waiting for Judgement's day to burn in hell, and decided to pay a visit at your school and say "Hi" or something.
Sorry I am not able to help... It's kinda hard through the internet.
Good luck (if I think of something i will add it later)