... It turned out to be his Ethernet-over-mains adaptors which he’d installed for his smart TV which was too far from his wireless router. I demonstrated this to him and suggested he stop using them but he didn’t bother. His house is a thatched cottage with thick stone walls and a stone floor making the use of ordinary cable a bit unsightly so I’m stumped.
The mush not only comes from his house, but it pervades my own mains wiring as well. >
...I could suggest he simply moves his wireless router nearer the TV? Allan G3PIY