Do you have any other devices apart from your router sharing the telephone line?
Do you have a filter between the telephone line and the base station?
And is that same line providing your BT Broadband connection?
No? From the box on the wall there are two outputs - one to the base station and one to the router
Do you know if it's a fibre broadband connection or wired ADSL?
It is the latest BT upgrade from 2012
Is there anything written on the socket?
A BT Group Business
Is one socket marked 'adsl' and one marked 'phone'?
There are no markings on either - the upper one is the internet and the lower one is the telephone
Do you have a filter - usually small white box with a lead and two sockets?
yes I do have a filter but I am wondering why the telephones changed last week to making a noise after over two years 'trouble free' and no filters?
Yes, it does seem strange
I'm thinking, if there is a filter in the socket, maybe it's failed
My other suggestions would be to try the phone with the router disconnected
and to perform a factory reset of the phone, but it will then require re-programming
I have tried with the filter on but no difference and likewise with the router disconnected
My wife is now calling me for dinner so I will have to go
Do you have a standard phone you can try ?
Shall I switch to Q&A, so we can follow up later
no I think I will take it back to the shop
He tried his best but ....
I thought you mentioned they were two years old - the factory reset may well work.