Here is a video that shows the problem between left and right monitors. Left is the one with the problem.
https://drive.google.com/file/d/1lJ-5Evx59Lp10QDqfpLUMRMk1hNnxkbY/view?usp=sharing
Especially after the sixth second it goes louder. Right monitor is silent as advertised by the company.
So, same here.
I bought from Thomann the KH120 ii monitors last month, two days later I have noticed the same noise coming from one of my monitors. I read your comments and immediately contacted Thomann to replace it. Thomann without question sent me a shipping label to send it back and replace it.
I took the monitor to the post office but it was closed so I came back home, connected the speaker again and the noise completely disappeared.
At this point I was confused because I didn't mark the faulty speaker and couldn't remember which monitor had the noise problem.
After about a week I have noticed the noise again but only for about 10 seconds when I turn them on or after it comes back from sleep.
On one day the noise became very loud for about 5 seconds, I could hear it from 3-4 meters or more...
So yes it does become worse with time....
Finally yesterday I sent it back... I have to wait 1 month before I get it back... can't do serious work.. not happy at all
But I really like how they sound, lots of depth and very small, I will give them another chance...
By the way my third pair of Ananda Nanos work great bought from the manufacturer, after returning the first two pairs that I bought from Thomann for making distorted noises at some frequencies...
Also my 4 orders from Thomann in the past 5 years all had at least one defective item... I am a little suspicious by now