To put my interest into perspective, I will document my experience with umbilical cables.
I lived 3 houses east of a canal in Scottsdale, for 21 years. On the canal road, there are also high tension electrical lines.
In July, you can hear these lines crackling from peak demand. I commented on this, talking with my neighbor one evening. He grabbed a 48" fluorescent bulb, and we walked over to the canal, directly under the power lines. He held the bulb in one hand and it glowed. I was surprised!
I was using a Pass Aleph P preamp. I upgraded to the Pass X1 with the full size separate power supply.
My equipment rack was full, when I had the Aleph P. I installed the X1 control chassis in my rack, with the power supply on the floor. the umbilical was stretched almost completely.
My system was noisy! I believe the umbilical was picking up the noise from the high tension lines. I re-arranged the X1 with the power supply directly below the control chassis, the problem was eliminated.
I'm sure there are other scenarios where RF, etc. can come into play. This was my experience.
I bought my XP-30 after I moved. I live in Tempe now, all utility lines in my neighborhood are buried. My system noise floor is dead quiet.