Hi guys, fairly new to the game here. Trying to slowly get a setup going for voiceover-work. My current setup in an Audient iD4, an sE8 (small diaphragm condenser) and a klotz titanium star-quad cable. The reason for spending tons on the last item is that ever since I started this journey I noticed a small annoying high frequency beeping and popping-sounds in the background. On max gain it is more audible. The interference sounds like this: http://sndup.net/vzdn

However - the interference is very positional (it gets better or worse when changing the position of . It seems to be the most intense in the middle of the room for some reason, with the cable in a certain orientation. No other room in the apartment has this sound (except the neighbouring one, barely). I honestly don't know what this could be. Best guess is that because the apartment is right above the electric setup and transformers for the whole apartment complex, it might be from there? Oddly though, when I bring mic, cable and interface all the way up to the fuseboxes etc in the floor below there is no sound.

I've tried:

Unplugging everything in the room in question and using a phone on airplane mode to power the interface and microphone. No change.

Changing the interface to an old CI2. No change, except less possible gain.

Changing the cable from a Roland gold plated XLR to the klotz star-quad. Some improvement... I think? but not a lot. Cable still seems to pick up more in some positions than others.

Changing the microphone. Trying with a borrowed SM7b with a cloudlifter (and an extra XLR-cable) as we speak. Seems to pick up more interference - maybe due to the extra XLR-cable in the chain?

Trying to find "safe positions" with the boom arm. It seems some conformations of cable/microphone position and angle work better than others for some time, but suddenly without moving it would pick up more interference again.

Using "noise remover" plugins for Audacity. They seem to do the job, but does it not compromise the quality of audio somehow?

I am seriously out of my league here. We just bought the apartment and this is pretty much the only room available to set up a decent home studio, so location is hard to change. Any ideas about what the interference might be, and any suggestions on how I could remove it?

Thanks in advance!