An Openreach engineer turned up without warning yesterday (Sunday!) afternoon. We were glad to see him because the noise on the line has been terrible.
He tested the line at the old 'Post Office' junction box where the drop wire enters the house, and there was still noise on the line. He then went to the end of our road and found that the connections in the box there were corroded "blue and green." Whatever he did to remedy it, the line has been pretty quiet since, and we've not had the same problems with getting an ADSL sync, or with the connection dropping (so far)!
The engineer didn't seem keen to do anything more than get rid of the noise on the line. So, we still have the old Post Office box. Thankfully, he agreed to leave the old extension socket wiring disconnected, so we no longer have a star wired set-up. With even more of my begging, he replaced the old master socket with an NTE5 (he said "they weren't supposed to, but he would on this occasion"). I'm very grateful, because this means I can now use the ADSL filtered faceplate I used at our old house, and if I want, I can run an extension from there for the router (wireless signal isn't great in this house). Great stuff!
I'm surprised engineers don't replace such ancient equipment (the Post Office junction box and the old master socket) as a matter of routine on these visits. Maybe they think "if it ain't broke, don't fix it." He did say that the old, ribbed drop wire was better stuff than they use nowadays.
Hopefully, no charge for yesterday's visit. My only concern now is, 12 months down the line, when we replace the front door, the window fitters will still have to work around the drop wire (which comes through a hole in the wooden door frame) and the Post Office junction box (which is screwed to the door frame) somehow... Or we'll have to pay for a 'service move' which will no doubt cost a bit.
Thanks for your advice, folks.
Barney