noisy Micro Modular mystery

[00schneider]

so i recently bought my second Micro Modular (in great condition, like new) and combining it with my other Micro Modular (a bit damaged but still works perfectly) was a great decision..

For a couple weeks I had the best time with both of them, but had to rearrange my studio at some point.
Since i did that, one of the two started to produce very loud humming / noisy sounds, even when the power is turned off AND the power cable is disconnected this sound remains. Tried several cables, different channels on the mixing desk but the sound would always occur when i connected it to the output of the Micro Modular (still not connected to a powercable).

If anyone has any clue how to possibly solve this please let me know!
I can't get my head around it because my other Micro Modular that i bought before the second one is way more "worn-out" but still very quiet compared to this one.

[catosim]

My first thoughts are grounding-issue.
Do you have a DI-box to connect the "humming" MM, and then try to lift the earth with the ground lift switch?
Another option is to isolate the grounding to the mixer, using some tape to cover the grounding pins.
If the humming disappears, then it’s definitely grounding-related.

[00schneider]

hey, thanks for your reply!
I solved it a few days ago, I have no idea why but it was the PC Out connection that was causing the noise. As soon as I connected it to a different Midi interface the humming noise disappeared and it sounded as quiet as the other Micro Modular.
There was nothing wrong with the interface I used before or the particular channel + I don't know how a Midi connection can produce such a sound, maybe someone here can explain this

[catosim]

I have experienced that the power supply to a laptop can cause humming on some occasions. When running only in battery the humming disappears.
It can be related to general grounding problem in the power network or bad or cheap components in some power supplies.