Help - Any Bt Engineers Or Knowledgeable Mse's

You may find THIS POST of use.

You can wire into the NTE5 socket yourself only on the piece that plugs in. If you undo the two screws, then the front should just pull out, what is left on the wall is BT's domain and this seems ok from what you have said.

On the bit you have removed will be all the extension wiring. Remove one wire at a time and and plug back in, as each extension wire is removed retest for noise, and you should soon find the problem extension, and this way you will find out which wire is to which extension, as the phone on that extension will cease to work.
If you are not happy doing that get a telephone doubler adapter and use that for your broadband modem and one phone. If you get a dect cordless then you can add phones without the need for extension sockets.

HTHs dc

Just a thaught but phone Bt and ask them if your exchange still has Aluminium wireing ..... Sounds mad but i had a similar problem while minding my mothers house in December expect eventualy the line just died, we called out Bt and the engineer came in plugs something in the socket and said he would eb back in 5 mins, sure enough he was, He advised us that in WWII they used all the copper they could get to make rounds / amo etc and as such they wired the exchanges with aluminium, after 45 + years these wires are burning out or corroding, apparently they wont re do a full exchange instead each time it happens they send an engineer out to put in 3 foot of cable for your line and then they wait for the next person to have a problem.

You need twisted paired wires for telephones. The reason for the pairs being twisted is to reduce the risk of interference and cross-talk.

Be careful not to lay the phone cables close to power cables as doing so could cause inductance from the power cables into the telephone wires. This results in noisy lines, commonly referred to as "white noise" or the sound of "fish frying".