Buy yourself an RTL dongle and a wide-spectrum omnidirectional antenna and run a spectrum analyser when the problems recurs. That will get you the frequency, ba

Buy yourself an RTL dongle and a wide-spectrum omnidirectional antenna and run a spectrum analyser when the problems recurs. That will get you the frequency, bandwidth and modulation of the interfering signal. I'm dismayed but not surprised that Openreach in the linked example launched straight into replacing sections of cable. They don't seem to spend much time actually analysing a problem.