Don't mind them. I've had a similar thing happen, but with power line Ethernet. In your case however, I'd be at least a little concerned about the building wiring.
That shielding was carrying noise from my PC, through the network switch, to my raspberry pi that I used for music streaming. Absolutely nuts.
I swapped to unshielded ethernet cables and it went away.
As for building wiring, this issue has persisted in multiple buildings.
Anyway, if you had problems with your unshielded cables that would be solved by a shield, but your shielded cables caused a different problem due to the bond at both ends, this technique of using shielded cables but severing the shield at one end of them would get you the best of both worlds.
If you're building an audio cable your signal will peak out at a few kHz, so the cable acting as an antenna and picking up a signal in the MHz range isn't an issue. Similarly, you're not transmitting anything significant either. But a ground loop can easily ruin your day.
If you're building a cable for multi-gbps data transmission, that ground loop noise might as well not exist - it's basically DC. But ground your shielding at only one end, and suddenly you're ruining everyone's wifi!
Building a device which needs high-speed data on one side, and analog audio on the other side? Good luck...
If you have a multimeter its probably worth double checking if the case is low resistance grounded to the end of the cord. I'm assuming you have checked already, but as a shock hazard it bares repeating.