Noise on line

[#1]

Morning all,
Following earlier useful advice I used DMT and tried to move the noise level down over the past months but it went up again. See current DMT attached.
My other half has always complained of noise on the line although I could hardly hear it and BT said the line was clear last year. So finally bought new phone did all the tests again and reported a voice problem. BT came out yesterday and checked the line and found it all OK when he rang from the exchange. He could however hear the slight hum and with his equipment when he listened at my master socket. He said  it  sounded likely to be electric as it pulsed but as their nothing wrong with the line that was all he could do.
It has had the hum for years although it is now constant he thought it might be the transformer in the street light which is very close to the BT box near the top of the pole.
Unfortunately the pole has the mains electric for the road and to two houses and a  workshop feeding off it but only my phone line so nobody to compare with.
In my tests I switched off all power for a minute to check if that would clear the hum. Would it make any difference leaving it off for a longer period to ensure there is nothing  in the house causing the problem. If so how long?
My semi-detached neighbour says his only transformer is in his doorbell.
If not worth leaving off the electric for say an hour  I will contact the council now and see if they will check  the street light.
Any other ideas?
Wuz

[#2]

Have you got any extension phones?
Have you tried plugging a wired phone into the test socket - and does the noise decrease?
If the answer to either question is yes, then the noise can probably be cheaply reduced.

[#3]

Yes, I tried two different wired phones into the test socket and the BT engineer plugged his device in as well. He ruled out any problem on the line to the exchange and thought the problem was external to their wiring probably electrical interference. I switched off the power to the house for a minute to check if it made any difference. It didn't so I am about to fill in a fault report for the street light outside in the hope it solves the noise level.
I will update with the councils response as the light works OK and there is no method of proving to them it is at fault.
Wuz

[#4]

You need to find out how the interference from outside is being picked up and fed into your router.
Internal wiring (extensions etc) can work as an excellent aerial at radio frequencies.
From the point of view of audible hum (probably mains induced) only affects a tiny portion of the broadband spectrum.
A while back, I had an external fault which caused so much interference that my phone was rendered totally useless as
a voice device.
But ADSL was unaffected - indeed I reported the fault to BT over their web site.
I wish you luck with the council.

[#5]

Thanks,
I have completed their web form. I will give them a couple of weeks to respond. I hope if I can get rid of the hum the SNRM will go down from the current 14.3dB.
Wuz