So I haven't caught any noise on the line yet but doing phone calls does affect the error rates. At the moment my US Margin is at 5.8 so not sure if that is the core reason, but the screenshots show CRC errors as soon as the call is up, you can see I made 3 calls.
It's annoying but I doubt I have anything I can report to BT and have a hope they will fix yet though, I presume it is not normal to get errors during a phone call or have errors on the line in general when presumably before there were none, but since I don't see a drop or hear noise and my sync is OK I guess they won't care about that?