Grounding issue between Intellijel 7U cases

Is there a way to ground the 0v rail between two 7U cases? Has anyone else had noise issues patching between two stacked 7U cases?

I’m getting a soft hiss from any jack on my upper rack. I don’t even need to plug in the jack. Just touching the patch cable’s tip to the outside of the jack will output a soft hissing sound.

I’m sending audio out of my Intellijel 1U stereo output, which is in the lower case. If I touch the patch cable to any jack on the upper case I get a soft hiss. Jacks on the lower case are dead silent. The problem is clearly in patching between the cases. But both cases are plugged into the same Tripp-Lite surge protector with the same ground. In fact all my studio gear (including the mixing board, etc.) are all on the same ground.

I’m using proper TRS cables for output, which I’m taking from the lower case’s TRS jacks.

There doesn’t seem to be much variation in the hiss no matter what I’m modulating. It’s not like noise I’ve experience before where a certain module seemed to be causing noise on the power supply.

Noise issues can be a pain to diagnose and can often be downright mysterious. It’s best to be systematic and try to gradually rule out things to determine what the actual cause is. If you eliminate the bottom case and use the 1/4" outputs on the top case, do you still get the noise? If you move things to a different outlet does the noise change? Is the noise coming through into the recordings or is it just going out the speakers? Are the speakers connected with balanced cables?

Might be best to deal with this through

I should mention that I use 2x 7U cases at home and often patch between them (and have done this at the Intellijel office) and have never experienced issues caused by bridging cases.