Noise from one of monitors near iMac

Question

Setup: a desk from IKEA, an iMac 27 2017 staying in the center, Steinberg UR22C connected to the iMac via usb type-c cable, 2 Yamaha HS5 active monitors are connected to the audio interface with balanced TRS-XLR cables staying right from sides of iMac.

The problem: once per around 5-7 minutes some cracking sound (it sounds similar to the one that is produced when you plug in a jack into an amplifier without muting it before, like thrrr-thr, crispy and loud one) pops up.

What's been checked already:

1. I've tried to swap L and R monitors, the problem persists on the same side(R), so it's not about some specific monitor
2. I've tried to swap the cables, the same result, the problem persists on the same side (R), so it's not cable related problem
3. I've disconnected the speaker (R) from the interface at all and it kept producing the weird sound! So it seems to be not related to connection to the interface at all!
4. So I left the speaker not connected to the audio interface at all and be only powered. Then I moved the monitor a bit closer to me, so its speaker became not on the same line with iMac, but like 30cm behind of the monitor's speaker and sound disappeared!
5. I've tried to change movement direction from horizontal to vertical and lifted the monitor to the same ~30cm (simply put some books under the monitor), but left it on the same line with the iMac and cracking sound persists :(
6. The volume of the cracking sound does not depend on volume set on a back side of a monitor as I understand

As for now it looks like a problem is hidden in a bottom right part of iMac (where a power block is situated i guess?) and position of a Yamaha HS5 monitor, but I have no clue what to do next and how to eliminate the problem.

Answer 1

So after a month of nerves burn I found a reason and solution and posting it here to save someone's time and nerves. Also it's free to try, so just try it :)

I found that speakers (both) affected by cell connection and produce this well known loud sound. So I've started to think about radio waves and.. what iMac transmits/receives? Bluetooth and Wi-Fi. I've started with Wi-Fi and ... it was it!

When you turn off Wi-Fi completely on your Mac all the noises go down too. If you use 5GHz Wi-Fi they don't appear back, but if only I connect my iMac to 2.4GHz network (we have it at home to support smart devices like vacuum cleaner, security cam, etc) it pops up and start cracking. So there are two options for me now: 5GHz only (which is fine) or wired connection.

Have a great time, googler!