Thanks everyone for your help.

So ..... I removed the extension wires from the back of the face plate on the main BT box so all extensions were isolated from the main box, replaced the face plate and still had the same problem with noise when plugged in to the face plate, no noise when plugged in to the test socket. So this suggests it is not the extension wiring that is causing the problem. So it must be either interference or the the face plate socket itself. So the next question is, if this was being caused by interference, wouldn't it effect the test socket connection as well?

That sounds like eckiedoo was right. .

You can get NTE5As, (that's what the faceplate is), at many places. You also (already) need an IDC/Krone tool for a couple of quid or less to reconnect those wires properly.

Maplin is one for faceplates, online possibly broadbandbuyer. Or get a filtered faceplate for neatness, plus an IDC/Krone from ADSL Nation, Solwise or Clarity.

Edit - It could just be the actual socket of the faceplate has got muck in, or its own plug going into the test socket is dirty or corroded. Is there any damp?

Edited by RobertoS (Sun 13-Jan-13 17:31:24)

My money goes on a dry joint in the removable faceplate acting to pick up the interference rather than a total component failure

Replacement faceplates are easy enough to source

Thanks, I have no direct experience of the NTE5, so was working from first principles.

Agreed about isolating the house wiring, I can achieve that in a slightly different way.

I have the older LT2(?), with all the Consumer side coming off the one plug going in to that. The plug leads on to a small distribution point for the various extensions around the house.

It was preceded by the very early version, with about a 1 cm square hole in the middle, a contact on each side, feeding in to various PLAN 4(?) sockets around the house. These were similar to the Jacks used on PBX's to connect the Operator's Headset.

That Master Socket was part of the original installation done in 1967 whilst the house was being built, the PLAN 4 extensions being about 10 years later.

About 1986, I had the line checked from the Exchange for early dial-up use for remote access to a main frame, PCW8256 purchased October 1985, modified to PCW8512 in August 1986., when the line was measured at about 23 db, typically 24 db today.

Thanks again to everyone for their help with this.

I have bought a new Master Socket and box from Maplin (Brand is Kauden and comes with a plastic wiring connector tool £13.00).

My existing box has the two banks of 3 connectors labeled 1 - 6 with connections as follows (after removing the bell wire, Orange- White hoops) -

1- Empty
2- Blue - White hoops
3 - Empty
4 - White - Orange Hoops
5 - White - Blue Hoops
6 - Empty

The new face plate has only three connectors, labeled 2,3,5. So you can see that this does not correlate with the above. Logic would suggest connecting wire with White - Orange Hoops (Currently terminal 4) to terminal 3 on the new face plate. Is this correct?

Thanks in advance for your help.

No, not correct, just use 2 & 5

4 is sometimes connected for neatness and if it works without the bell wire fine, if not reconnect Or/Wh to 3.