Ongoing issue concerning intermittent noise on lin...

Question

I do not seem to be having much success in getting BT's overseas call centre to deal with this issue, so I would be very grateful for any help on this forum, please.
Since October last year, I have had intermittent broadband dropouts. It reached a stage where they were happening every 24 hours. I thought they were resolved when I bought a new router (I have always used third-party Netgear ones, I've never owned a BT HomeHub), and changed the cabling, but the problem has worsened during the last few days, especially the windy and rainy weather.
On picking up my telephone handset, I noticed very loud static on the line, which made the dialing tone almost impossible to hear. On one or two occasions, the broadband connection dropped at the same time. I have tried the test socket - same problem. The static is intermittent, not persistent.
Following the advice on these forums, I raised a voice fault initially. An engineer called yesterday, ran some tests on the line and said there did not appear to be anything wrong, and advised me to report it again as a broadband fault if the problem re-occurred. He also fitted what I believe to be a Mk 1 BT Openreach filtered ADSL faceplate. He said as the fault was intermittent, it was "very difficult to work with".
All seemed well with the new faceplate until about 10pm on Friday. I happened to pick up the phone and noticed more static on the line, and my upstream noise margin dropped from 6.7 db to 0db. At the same time, the modem resynced, and the static cleared after about 30 seconds. The connection does NOT drop every time, though.
The call centre has raised a broadband fault, but the line went mysteriously dead during the call (I was speaking to them on a separate line, not the one affected), and no-one from the call centre bothered to phone me back. I already had to explain the problem TWICE to them. Very frustrating.
I really don't know if this is a high resistance fault, something wrong with the equipment at the exchange, or what? The engineer who attended made no tests for broadband faults, and said that the broadband tests were much more complex.
I'm stumped. I wonder if a moderator or a knowledgeable person here could please advise me further? I really would like this resolved.
Many thanks.

Answer 1

Many thanks for your reply, imjolly. I've checked the cables and positioned the router away from any possible sources of interference.
Further to my earlier post, I tried another telephone handset this morning (an Opticom B300) and noticed that the background hiss was almost continuous this time, while the router was switched on. There was no crackling, though, and the connection did not drop. But when the router was powered down, the line was much quieter.
I'm guessing the broadband signal is starting to "break through" to the voice signal. That shouldn't happen, should it??
I went back to a BT Decor 110 handset (the one I always use) and the background noise was much reduced, even while the router was powered on.
No dropouts so far. I'm no expert in these matters, but it's almost as if an electrical charge begins to "build up" on the line, and then I will get a "storm" of static and crackles for up to 30 seconds. Then a loss of sync. Could be any time of day. Still stumped!