Malekko 8NU8R

I recently started w modular and use the Malekko 8NU8R to get out audio to my speakers.

The issue is that as soon as I (accidentally) thouch the patch cable from the 8NU8R to the speaker the speaker starts humming and I can only stop it by unplugging/re-plugging the speaker. I have different cables from different manufacturers--no joy.

When I patch the cable to my Focusrite 2i2 soundcard instead and from there through the laptop/PC to the speaker all is fine and there is no humming if the patch cable is accidentally wiggled.

How can I improve this?

That sounds like a ground loop, actually. Do you know if the powered speakers are on the same AC ground line as the synth, or whether they're grounded at all? If not, that would explain quite a bit.

Probably the best thing you can do is to take the time (and hookup wire) necessary to set up a star-ground to get all of the equipment on the same ground plane. It's time-consuming, but very worth it in terms of cleaning up noise and hum, and might only be necessary for a few pieces of your gear. Have a look at https://www.sweetwater.com/insync/star-ground/ for a very basic explanation of what needs doing...and as I noted, if you can do this only with certain offending devices to clear up the ground loop issues, that works just fine as well.

This could also be a bad jack in combination with grounding issues. To help troubleshoot, when the humming starts, try touching a wire to the lip of the jack at each end of the cable at the same time and see if the humming goes away. Also, does additional wiggling of the cable ever stop the humming?

The thing w the wire touching the lip of the jack is not really doable on both sides because one side is an XLR (if I as non-native speaker understand the meaning of 'lip' right then there is no lip :D). The humming stops if I carefully wiggle the cable and then take care not to change its position/not to wiggle it any more.

What surprises me: it really sounds like a ground loop issue, but today I tried a 100USD hum eliminator and this had just no effect.

There is no humming if I plug in a headphone into teh 8NU8R, the humming only occurs with my active speakers.

Had a look at the 8NU8R specs. Is the hum occuring when you have your output plugged in, but no input into the 8NU8R? If so, then what you're running into is normal for the module, since it's designed to output an offset DC voltage when no input is present. Headphones might not pick up on the humming, but with something active such as a preamp stage (as in the Focusrite box), it's going to be brought up to audio levels...and then some. Plus, running DC offset directly into a preamp, depending on the type of preamp, might not be a good idea.

Really, that module isn't designed to be a proper output, upon closer examination. A proper output is something more like this: https://www.modulargrid.net/e/pittsburgh-modular-lifeforms-outs where you have a ganged stereo attenuator and 1/4" outs, possibly also a separate headphone amp, and the like. While the point about the star ground I made earlier is also valid here, using a proper output module is probably what's actually needed.