Just tried a couple of cables, same results.  Most are "official Doepfer" , the rest are generic eurorack cables from a reputable source (Analogue Haven).  No 1/8" stereo cables in my set up.

Grounding could very well be a potential cause.  When I'm finish with work for the day, I'll try pulling these off the shelving to a different surface.  I'll also check for any loose wires from other systems which may be touching one of the machines /shelves in back. It's be great if this turns out to be the problem as my road cases start arriving this week. (goodbye shelving with desktop racks!)