Effect of Internet Service Quality on Streaming?

@lalitk , I have a Muon Pro, two Network Acoustics ethernet cables, and a Tempus switch on order, to replace my Innuos PhoenixNET and two Audioquest Diamond network cables - assuming I don't return it all in 30 days that is....

That said I still don't know at this point if my issues are due to network degradation (which I DO see on measurements during periods of bad quality), or AC power noise, or both.

I've downloaded from HDTracks a 16/44 version of a test track I use a lot and put it on my server.  Right now, both the Tidal streamed version and the local file sound fantastic.  Different, but both great.  A bit better image specificity on the local file but really I enjoy them both.  I will wait until I get crap quality again, and do another comparison.  If they are both bad, I suppose it means AC power noise is the limiting factor.  If the local file is much better, then I will 1) see if the Network Acoustics gear changes things when it arrives, and 2) follow up with my ISP as @hgeifman suggested.

@nyev my system is plugged into two dedicated circuits. The sound is better after 11pm. Everything is quieter, my family members including my dog are not running around. Sound is fantastic. I tried Ethernet filters (N A Eno streaming system) and it changes the sound yes, but does it filter anything? May be. But it didn’t mitigate the lower performance of my system until that quiet moment after 11pm comes. 
So in my opinion it’s a mix of everything that uses electricity in your house plus people who quit disrupting our listening before midnight. Doubt it’s Ethernet/internet quality. 

@audphile1, I think you are probably right.  I was hoping that just maybe, it was an issue was something I could address, if it was related to my network/internet.

I don’t think my issue is ambient noise; my system sounds almost as good most of the day, it’s just the 3-5 hours around dinner time that is an issue.

High ping times are fine, it’s error rates and high jitter (> 300mSeconds) that can cause issues.  Large ping times may make a stream slower to START but once started don't add up over time. 

500 Mbps is more than enough to stream just about anything.

IMHO, only really poor streamers should have a problem with Internet conditions you’ve described. They usually have several seconds of buffering built in, which can sometimes be configured, which should eliminate all but the worst kind of connections.

IMHO, again, it’s much more likely to be a power issue.