After reading up on this phenomenon I wanted to test this out in the real world. I first thought of optical converters from switch and into my streamer (I know some streamers got optical network support directly) - with fiber cable between them. Then I though of the cheaper alternative - to use wifi. I also read multiple places that wifi were no good; due to often bad implementation of wifi in most streamers which actually lead to more noise internally in the streamer than the noise coming from a switch with noisy power supply.
Regardless - I first started to detach the ethernet cable from my streamer while playing (it got a buffer, so it plays for while without any connection). Here I found to my big surprise that the quality changed to the better. So I dug up the wifi-antennas for my streamer (Moon MiND2 Network Player) - and gave it a go with wifi and no ethernet cable connected. Same effect here; much better sound. And since there are no dataloss over TCP/IP - this can only be because of noise over the ethernet cable (either from environment picked up by cable or from other devices connected to the same local network).
Recommend everyone with a streamer to test this out. The difference in audio quality is big; with ethernet cable connected the sound got “muddy”. Sound quality is really great with ethernet, but so much better when using only wifi.
Please share experience you already have; or you find while testing this. My guess is that it will depend on equipment used. Some are far better over ethernet, other via wifi.
During testing I used a fairly high quality shielded 1.5 meter CAT6 cable. I also tested a selection of other ethernet cables; same result.