Am having issues with poor quality phone line on internal sockets, really bad hissing and sound like car engine. Have a BT Open reach NTE5C Mk4 master socket. Quiet line test in back socket is fine. Have disconnected all internal wiring from socket then plugged wired phone into face plate and still get interference. I thought this proved the socket face plate was faulty, bought new one, internal sockets still hiss bad.
So, I'm now looking at interference at master socket. It's located in ashlar walls in roof of our dormer bungalow. The Cellotex roof insulation is foil backed and actually touches the edge of the socket. Could this be the culprit? Or if the cabling from the pole runs close to the foil insulation could this be affected? Any suggestions welcome.