Help - Mystery Hum that starts at my Streamer

If you have a Cat 8 cable swap it out for a Cat 6    The Cat 8 cables are grounded via the metal connector.   I was told that Cat 8 can cause problems with ground loop in some situations 

Has the system previously worked without issue and this is a new problem?

Oddiofyl - thanks for the suggestion, I will give that a shot.  That’s the one area I handle swamped anything out on except removing a noise filter.  

I have a home run Ethernet run from where my modem and the switch sits to the streamer, if that’s Cat 8 would putting another switch in and feeding the streamer with cat 6 elevate a potential grounding issue? 

Cleeds - thanks for the quick response.  I noticed the hum once I swapped out the Krell Pre for the Leto.  That’s when I tried my Anthem HT receiver as a pre and going direct from my DAC.  Only combo that elevates the him is with the Krell Pre in the mix.  I should mention I swapped out all the tubes in the chain - DAC and Leto to ensure a faulty or noisy tube wasn’t the culprit. 

Weird... if you have a USB source, disconnect it.  I have seen those cause audible as well as jitter hum.  My own term for worse jitter due to a ground loop.

Usually you don't need to use an Ethernet isolator, except if there is a shield connected at both ends.  The hum present from a USB or Ethernet ground loop is usually present even without music, so unplugging the Ethernet cable should help you diagnose it as a potential source.

I use one of these to isolate my Ethernet and to improve the surge protection:

PS - Before you ask, recent studies on internal Ethernet surges suggest against grounding the cables but that isolating the cables minimizes surge damage. Grounding a surge in an Ethernet cable gives current a place to go, which is bad when it runs through tiny wires in the wall.  Better to isolate the Ethernet and let a surge find a path to ground via a power supply.

Thanks for your comments Erik!  I have the Ever Star in the chain and I have unplugged the Ethernet cable, hum is still present.  Had forgotten I had tried that during my process of elimination.

Maybe it is the upgraded power supply, unit has an internal supply and the upgrade is internal.  Only variable I can think of that I haven’t ruled out.  
 

Happy NewYear.