I had exactly this. Twice!
I reported it the first time, and they ended up changing my connection at the cabinet to a different pair from there to the exchange. That fixed it for a while, but it also caused me a permanent loss of about 700kbps from my previous ~6500kbps.
Talking to the engineer, and confirmed by a few others seen at the cabinet since, I found out that the cable(s) from it to the exchange are in a really bad state. Even connecting a new phone subscriber, or swapping to a different pair like was done for me, takes them an age. Phone mind you - never mind broadband.
They sit there talking to base, and get three unused lines suggested. They test them, no good. Another three please. And so on and so on.
It started up again, and gradually got worse, until it was more than once a day on average. I used to use the Quiet Line Test, 17070 Option 2, as although ringing anything fixed it almost straight away, I needed to keep the call going for 5-10 minutes to make it stick.
Fortunately it didn't affect my connection speeds as I was on O2 LLU, that doesn't have the BT Wholesale DLM.
I waited as long as possible, as I didn't want an even slower pair. Then I was lucky and FTTC became available, cutting out that that section of cable for the broadband. So I went for it. Fine ever since, and never notice any phone line noise either.
That option may not be available or practicable for you though
My broadband basic info/help site - www.robertos.me.uk
| Domains,website and mail hosting - Tsohost
Connection - Plusnet
UnLim Fibre (FTTC). Sync ~ 51.8/16.8Mbps @ 600m. - BQM
"Where talent is a dwarf, self-esteem is a giant."
- Jean-Antoine Petit-Senn.
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