the question of changing ethernet cables

“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.

@finnlove Believe you're speaking of Small Green Computer, specialize in optical steaming. I do use Sonore OpticalModule and OpticalRendu, many experiments with optical in past and continuing into future, some in next few weeks. With optical you can go with generic or Sonore FMC in which case you could go full optical from ISP through streamer, this may or may not beat any ethernet solution, hard to say, implementation is key.

Now, if you had optical capable router and all Sonore optical, fully optimized this could be very nice setup, full galvanic isolation from wifi or any other noise. You would still have issue of wifi directly injected into router motherboard which cannot be elimated by any means other than turning off wifi on router. I bet you'd have pretty nice setup going this direction, I'd at least try if I had optical via ISP.

Keep in mind optical not so easy as install and forget, subject to optimizations and improvements just as any ethernet setup. I won't go into it here, but suffice to say Sonore equipment superior to the generic FMC. My further upgrades, already in house will come in due course.

Shoot! Yes, I did mean Small Green Computer. Good sounding solution and agreeable price. However, 81 Euro shipping cost is unrealistic. In the event of ethernet upgrades, I will have to look locally. I can see this needs to done by the logical explanations here. Yes, we do have a series of small lights in the ceiling. This could produce some infect as mentioned.

Another good point (Lalitk) check the gas before changing the spark plugs. I do have a new amp from PS Audio - BHK Signature 250 Amplifier - it is a hybrid with tubes. I will check with similar threads to see the FB. I just put a Shunyata Alpha NR on it. Most of the interconnects, where critical, are Cardas. I have MIT 16 speaker cables to the Focal Sopra 3 speakers. I have the PS Audio DAC/streamer and PS Audio SACD. Preamp is the primare S P32 that has no tubes. Planned is to replace with a Trinnov Altitude 16 for Home theatre. To this end I have a 7-channel Primare amp but it is not on for music. Likewise for movies only is a Primare A32 for special effects or rear surround, Atmos. Surround speakers are the Klipsch 500 series and Atmos Klipsch 400 series. Speaker cables are very heavy gauge wiring due to the distance. Again, only used with movies. Same with the B&W 855 subwoofer with upgrade. In all of this, NO, the ethernet cable is common and not shielded. Other mains cables are stock - planned is supra shielded cables. All of my cables are isolated and run through cable channels for separation and no crossover possibilities. Same as in the wall with the new wiring, they are each run through their own channel. I do not have a power conditioner yet. I am looking PS Audio 15 for the future.

The router is from the phone company and was first produced by huawei It most likely stock. I am looking into this as well. I found a dealer in the Netherlands. I'll let you know what they say.

@sns I like the idea of your upgrade going optical. As I seem to be developing a real tick for this stuff, I will look into that for the future.