Massive jump in noise margin

[#1]

Hello,
I've had a long running problem with my broadband that I have previously discussed on this forum, thinking it was a speed fault. I ran all the normal tests, changed my filters & router and ran from the test socket.
BT eventually came over a few weeks ago and changed the master socket to an Openreach one, upgraded the connections at the point the line comes into the house in the grey box on the wall outside (they were previously heavily oxidized copper blocks and are now silicon) and apparently renewed a very elderly cable in the green box down the road. I saw a jump in speed immediately from this work. (There are no overhead BT lines in my area, it's all underground cable so we can't see what the rest of the line is like)
It now appears it's an intermitent connection fault as I'm getting random dropouts at various times during the day and night, causing me to synch at low speeds.
I've only physically caught it doing it once and could see that the ADSL status light was pulsing on the router. The rest of the time I pick it up from my router log.
My new router shows me more stats than my previous one did and I've noticed that usually the noise margin is around 15db, about 13db up and 16db down. The attenuation is around 30db up and 60db down, so it's a long line. I usually synch at just over 2000k and up until about 9 months ago had a very stable 1500k connection for several years.
What I've been finding is that my down stream noise margin has been jumping to 22db and the synch speed plumets to 600k. I reboot the router and usually it resynchs and returns to the lower noise margin and 2000k speed and can last like this for a day or so before changing again.
The time I caught the router flashing I was able to determine that nothing had been changed in the house, no lights or equipment switched on, the central heating off etc, so am just really confused about what could be causing it.
Is anyone able to suggest something I can try to identify the problem as it's driving me absolutely crazy.
Thanks and best regards
Simon

[#2]

Hi, quick update. This evening the downstream noise margin has dropped to 9db and speed 800k. I've never seen the noise margin so low and am now thoroughly confused!
Any advice would be very gratefully received!
Simon

[#3]

Hi Simon,
There's a few tests that can be done on the faults blog here - if that doesn't turn anything up (apologies if you've already done all that) then the only thing we can do is raise a fault I guess.
Hope that helps,

[#4]

Hi Matt, thanks for the response. I've got a ticket raised and have now got to the BT engineer visit stage again. I really struggle to get time off work on weekdays so am trying to avoid having BT over again. Also since it's intermitent I'm not sure if they'll find it when they come. I'm going to buy a third microfilter just in case but I can't afford a third router, so will see if I can borrow a friends just so I've tested everything twice! Best regards, Simon