It does sound like there is an external line fault, and there is nothing you can do about it, other than ask your CP to fix it.
Meanwhile, I’d not swap any phones, or filters, or modems, just leave it all alone, and report that there is audible noise on the phone line (if there is). If external, it is not a problem that you can fix. But by continuously swapping appuratus you may be confusing the symptoms, maybe giving the impression it is broadband fault rather than a line fault, and making it harder to get agreement that the line itself is faulty.
Sorry for the late reply. Indeed, it does sounds like it but sadly the test refuses to pick up a problem. I've started an 'extended line test' from CIX's control panel which will run a line test every 4 hours for 24 hours, but I highly doubt it'll find a problem still. DLM intervened last night and has relaxed the error correction on the upstream (from INP 4 delay 8 to fastpath). Downstream is still interleaved but hopefully that'll go back to fastpath within the next few days. The connection is capped slightly in order to try and help encourage DLM to switch everything back to fastpath possibly a little quicker.
At the moment I can't hear any noticeable noise on the phone calls and nobody here is reporting any unusual noise, but at least 50% or more of the time I make or receive a phone call I usually encounter a drop in SNR (especially for the U1 band). I can't imagine this is normal, but at the same time I don't imagine it's something that'll convince Openreach that something isn't right.
See the images at
https://imgur.com/a/b2XVGoh - Comments from anyone are welcome. I will contact AAISP next week and see what they suggest too, hopefully by then the downstream will be back on fastpath again and so it should then be easier to see errors on Yukon in the event that I might get plenty of errors. The blips in SNR shown on the graphs are when someone made a call this morning and the most recent one was when I received a brief call.
Also one other thing maybe worth mentioning, the downstream FEC errors have been constantly at the rate shown in the above URL since around 11pm last night, prior to that it was just the odd blips of up to 1500 ish but most of the time just a handful to a few hundred downstream FEC errors.
I've not changed the filter or cables for the last two days or so, the DECT phones (recently purchased BT Advanced Phone Z) are also connected. One last thing I tried recently was to reposition some of the equipment inside my server cabinet in case something was causing some kind of interference. Sadly it hasn't made any difference.
