What happens to the phone line if you plug the router in but don't power it up?

I'll give it a try.

I think it won't make much difference.

Disconnecting the ADSL connection through the routers screens is enough to make the noise disappear.

I suspect with the modem powered off the voice line will be good.

Only suggestions to your end...perhaps worth to try
If you have the modem near by a tv or speaker or any electric device etc, remove them far, also if you have it at an extension electric socket, plug it direct alone
https://support.zen.co.uk/kb/knowledgebase/broadband...
That may helps to have less noise stress at your situation

Change rj11 cable from phone socket to modem ... even if is sealed or grounded i think may still cause issue by trapping additional noise if the rj11 port at modem is not grounded, so try with an ordinary rj11 cable

i hear a BT 80B RF3 Junction Box works in some cases even if is for different purpose (i think needs to be installed before the master socket & i know you have tried filtered plate but it may makes difference because contains coil so more realistic in your case?) and also try this time 2 filters in line (connect them at the phone indicator)
It will not fix the issue if is from isp /line but it may makes little better the situation

Edited by deleted (Mon 20-Jun-16 09:42:21)

If the noise occurs with two different modems/routers only when they have established a DSL connection, then I did wonder whether there is a faulty port at the exchange which generates noise when it is replying to your equipment.

Have you tried asking your ISP to get you connected to a different port?

Just a possibly daft suggestion. What happens if you replace that shielded cable between the router and filter with a bog standard DSL one? AIUI you introduced the shielded cable whilst the engineer-fixed remote fault was present.

Well I have eliminated the shielded cable and the Billion 7800N router by plugging in the home hub that BT sent into the test socket using alternative filters and still get the issue.

Its sure got to be something between the house and the exchange.

One engineer "Robert" also rigged things up so the copper pair came straight from the overhead wire through the first floor window to my router and still saw the issue.

So this really takes out the length of cable down the side of the house, the junction box as it comes in the house, the cable to the master socket and the master socket itself.

I guess it would be useful to repeat that test with the home hub BT sent just to absolutely prove the issue is outside my house.

Engineer coming tomorrow - be really great to get "Robert" again as he has been the only one to methodically work from the house to the exchange - none of the others seemed to want to investigate outside my property.

The engineer that turned up was booked as a "broadband boost green" job so did nothing more that test - decide it was ok - and leave.

At 9 that morning the voice line was as scratchy as ever but by the time the engineer arrived there was nothing to hear.

Next they are going to send a voice engineer and a broadband engineer at the same time.

Again I just hope that they are prepared to venture out of the house and along the cable toward the exchange and investigate the state of the network rather than constantly trying to prove its a customer premises fault.

Have you got a sound recording of the noise?

Play it to them if it's not noisy at the time?

I'm sorry, but that is a futile gesture .... Who's to say that the recording is even of the line in question.

I just thought it might help them identify the problem based on the noise, if they've seen (heard!) similar before.