Here is an explanation by someone far smarter than me that maybe shows why I prefer music through the pi3 usb via the usb to ethernet adapter versus from the ethernet port directly:
The big, big, big issue with noise and Ethernet on the Pi is that the Ethernet transformer center taps are tied to the Raspberry Pi 3.3V plane. It has a ferrite, but that is to keep out noise in the MHz range and up, not in the audio range. In fact, the purpose of the center tap is to shunt common mode noise to the power plane!
