When you remove the front faceplate you are disconnecting all your extension wiring, if there is noise when the extensions are connected but not from the test socket when they are not, it indicates there is a problem with your extension wiring that is causing the noise. Internal wiring is your responsibility not BT's.
OK I understand, thank you for all your help but there is not much I can do but to call an engineer in thanks for all your help as I have learned quite a lot today
Thanks for the help guys, engineer came round and indeed it was the interrnal wiriring at my home that was the problem and it has been fixed, now acheiving full speeds
Glad you got it fixed but expect a £130 bill for the privilege.