Noisy ethernet cables

@erik_squires ,

Except the Ethernet connector, metal shell, where the connector plugs into, is usually connected to the metal enclosure to improve the EMI. Even before shielded Ethernet cables were common, most connector shells were metal to form a seal with the metal enclosure for EMI purposes. I am well aware of Ethernet implementation (hence why I know POE is galvanically isolated if done to the specification).

Signal grounds very commonly have capacitive connections to case grounds where they exist for noise reasons.

In the average home environment, unless you are co-running your Ethernet in long run in parallel with a seriously noisy AC like in industrial/commercial, there really is no need for shielded. There simply are not the noise sources to make a difference. As you noted, it is already galvanically isolated.

Except the Ethernet connector, metal shell, where the connector plugs into, is usually connected to the metal enclosure to improve the EMI.

That is entirely up to the equipment manufacturer.  I have a hard time believing a high end streamer maker would both ground for the sake of better EMI rejection AND leave themselves open to ground loops.  I certainly wouldn't design a mixed digital/analog device like that.

@erik_squires , I would have more faith in a lower cost, higher volume product from a lesser vendor, that has the proper equipment for testing, and probably more experience, that a boutique vendor who in many cases is winging it.

I am not saying that is exclusively the case, but measurements by Stereophile/ASR have shown enough "high end" equipment to have questionable performance, even on the basics, that I have some confidence that is correct. I would expect the larger high end vendors to be designing "properly", at least I would hope that is the case. Fortunately, this is an easy one to test. Measure the resistance/capacitance from the Ethernet jack -shell to the case.

Also, to be clear, I'm less worried about noise getting INTO an Ethernet cable as much as it radiating to audio signal cables.

@erik_squires ,

With the twisted pair, you wound need to be running them pretty close. Packet bursts could demodulate to audible frequencies so there is a mechanism for the noise transfer even if the transmission frequency is high. I suspect this would be not much of an issue at 100M or 1Gig, more at 10M though since those high frequencies would be too high to even be demodulated as bursts at the power level.