the question of changing ethernet cables

@finnlove 

From your description I would guess that the problem actually stems from your router: do you use it for wifi? Can you turn wifi off? Can you use a linear power supply for the router? What model do you use; can you try to upgrade? Also try a Lan isolator, my preferred solution is Pink Faun. Alternatively EMO or Acoustic Revive work well, too. 

RFI/EMI does normally not result in white noise since it happens at much higher frequencies and modulations at that frequency range would be very weak. More likely this is noise coming from the router‘s power supply.

Thank you antigrunge2. Everything is in the attached garage, modem, router and this station system to extend wifi. Meaning the main station extender and the slaves are positioned around the house for better wifi.

The router is plugged directly into my fuse box. I have outlets built in. I can see from the wire pile up and the proximity, as well as the use of, the fuse box could add to the noise.

I just started to read about your suggestions. Pink Faun is produced in the Netherlands, which is very close to me. There is also a dealer I found in Germany. It diffently sounds like I need to add some type of filter post router and a filter converter to fiber. Then a fiber cable to the streamer/DAC. That was green computer's solution as I understand so far.

As I said, I am still looking at Lan isolators. I do have to say, this is quite an interesting science. 

“I have just the amp and preamp on I have a very slight hiss”
@finnlove

I suspect that white noise / hiss your hearing is coming from router. Without knowing every single component in your system, we can only speculate. I used to own a tube amp that produced a very faint hiss, I could easily hear it when I am near my tweeter but otherwise inaudible few feet away. As you said, hiss is already there when you turn on amp/pre. The noise is further amplified when you turn on streamer. I would look at each and every step in your signal chain i.e. interconnects, speakers cables including LAN cable.

Before you drive yourself crazy and spend more money, do you know if your electronics are supposed to be dead quiet? Contact the manufacturer or read other users feedback. Are you using a power conditioner in your system?

The most common reasons for hiss is poor grounding or gain stage in your preamp. It could be also from poor wiring or EMI/RFI in your environment.

+1 what @lalitk and ​​​​@antigrunge2 Said. The entire chain is key. Quality cable with quality shielding, isolation, quality modem and switch. 

@finnlove Any dimmers/reostats anywhere in house can cause these sorts of hissing/fuzzy sounds. Even with dedicated circuits on audio these can infect, transformers with LED lights can also infect, I know both from personal experience.

Otherwise most likely culprit tube amps, pre's. Doubtful SS equipment would cause this. I've never heard any hiss  noise emanating from various routers or modems with or without lps, still, who knows whats possible with these streaming setups. Connecting directly to fuse box like you have may actually increase susceptibility to noise.

In regard to possible router noise, just a couple days ago installed  Netgear XR1000 router, this for lower ping time/latency/jitter vs previous Netgear R7000. So new Netgear now direct feed from modem, also now only feeds streamer, NAS and R7000. XR1000 wifi now turned off, R7000 feeds all wifi in house. Point is to get all wifi with it's extremely high levels of emi/rfi completely out of streaming chain. So now I have optimized my entire chain feeding streamer, best modem possible for my particular ISP, all wifi off system with high quality router, ethernet filtering/clocking via JCAT Net Card XE, quality cabling via all AQ Vodka post modem, everything running off high quality LPS. All upgrades prior to latest wifi isolation have been effective in lowering noise floor and more analog like sound via lower jitter. This weekends listening sessions will determine the effectiveness of new router and wifi elimination from streaming chain.