Weird beeping sound

It's been almost a year since i posted about the beep, and i have had no replies. Reviving since its STILL happening.
So i recently picked this game back up, and within ten minutes i was hearing the beeping. I come with new information on it this time.

In the Linked video, you can very clearly hear the beep at about 3 seconds in. (I have to use a link since i cant upload videos to the attachments for SOME REASON.)
https://streamable.com/gq5frp    (might have to raise your volume to hear anything)

its a weird rising then falling noise. sometimes its faster, sometimes its slower. It happens seemingly randomly, and at random speeds, but always the same pitch, same rising and falling, and ONLY happens when there's stuff going on. it NEVER occurs when you're just standing still or walking around casually. you need to actively be in combat OR in an alternate form.

@Mysterymaster_OP  I wouldn’t have seen your post a year ago because I hadn’t even joined the forum back then, so I appreciate the bump.

I tried taking a look at the video link that you had attached, but unfortunately, I couldn’t access it and I got an error message. I have attached the error message here. 

Is is it possible for you to provide any more information, or is that all the information that you have got on this strange noise so far?

@Mysterymaster_OP
Your video link seems to be broken, Following error comes up: "Oops! We couldn't find your video."

Streamable decided to reset all my videos, so here, have a youtube link instead.
https://youtu.be/mYI_KkD7qyA

New Information on when it occurs:
https://youtu.be/o8Yp8V-OvsI

Happens VERY consistently with cactus, though im not sure of a pattern since it happens both with crit kills and normal ones, and sometimes doesn't.

hold on.... i have calibrated on my cactus, and the sound stops happening when i switch off of calibrated.
is... is the beep the sound of an upgrade activating? if so, im assuming it only happens with upgrades that you cant immediately see an effect, since its not instantly obvious that calibrated has activated... am i correct? what are the conditions for the beep to happen if im right?

@Mysterymaster_OP  I’ve watched your video and I know exactly what noise you are talking about now. I’m guessing you need to have particular upgrades equipped. I have heard that noise before while using Snipers and I have used the Calibrated upgrade before, so it is possible that the upgrade is creating the noise. I’m not sure - maybe I should also test this myself.

It could be the XP