You could try iFI silencer and see if it helps. Personally I would avoid PoE at all cost, why add more noise only to remedy afterwards. Instead, try mesh network pods (you need two, one next to router or modem and 2nd receiver near UltraRendu).
Reducing noise in an Ethernet over power configuration
I don’t have the luxury of a separate Ethernet outlet for streaming so I’m using PoE. I’ve never been impressed with the sound quality of my EtherRegen feedin my Sonore UltraRendu. I’m seeing products from iFi Like the silencer + that coul eliminate some of the noise. Has anyone used one of these products for this type of application?