Patchbay grounding advice

Please feel free to move this if it's in the wrong forum.

I have a problem that has bugged me for ages. I have 24 channels of mic pre-amps half normalised with a Neutrik soldered bantam patchbay to 24 inputs of my Lynx Aurora converters.

I get pretty bad hum when I record like this but when I join the pre-amps to the converters with patch cables it is silent.

Any ideas why this happens?

It isn't an issue most of the time as clients track with outboard and just breaking the connection and patching in a few compressors and EQ's makes the hum go away. Even without any outboard it is easily fixed with patching but it is still annoying and I would like to get to the bottom of it.

This is where people chime in with ideas that are not applicable because they don't understand exactly what the problem is. Post a drawing so that people have something to visualize. Print this out:



and draw in your gear with the exact wiring to the mic pres, outboard gear, converters, etc paying particularly close attention to shield wires and grounding points. For example, are the shields not connected like in the above drawing (which I just pinched from Google images so I don't know why they're not or if they should be)? Then take a picture with your phone or scan it or whatever and post it here.

We can almost definitely figure out where the noise is coming from. The process for debugging noise issues is actually pretty straight forward. But if you post a good drawing, it will make the path-of-least-resistance to a diagnosis much shorter.