sounds like high ressitance fault and you need to report a phone fault to 151 get sorted and broadband will be ok
are you using the master socket and not an extension socket? the master is normally the first socket in your home where the openreach wiring enter from outside
If you don't have a test port then it's possible that it's not the master socket you have taken the cover off, or it could be you have a LJU ( line jack unit ) master socket that pre dates the NTE5 type sockets ( NTE5 type became standard kit in the early 80's) ...or it could be a decorative , non standard socket.
It isn't as easy to isolate the 'line' from the internal wiring with LJU's , required to establish if a fault is outside or not, outside is Openreach's responsibility , from 'internal' , which is your own responsibility.
As far as the noise reducing temporarily, if you pick up the phone , then clear down a few times, there is similar situation where receiving an incoming call does the same thing (makes a noisy line quiet for a short time ) perceived wisdom seems to be that the extra current flow through a high resistance connection , lowers the resistance , but it soon returns ( as does the noise created by the HR connection) ...best to establish as far as practical if its external to your property , then report your line noisy to your landline rental provider
here's the pics of the master socket, it was replaced after a fault in the very early 2000's. I don't seem to be able to see a test port anywhere.
The line still continues to be very noisy, thanks again for all replies and help.
You don't see a test port because the socket isn't a NTE5 type master socket, its a line jack unit master socket.
FWIW, it doesn't appear to be wired optimally for broadband performance either, if you have extension sockets and don't really need them, I would identify the -50v battery and earth from th exchange , they will already be connected into terminations 2 and 5 , possibly alongside other wires that run to an extension socket , it's difficult to tell from the photo , you don't need anything on any other termination apart from 2 and 5, the wire on terminal 3 may be slowing down your broadband speed , and it's possible that your noise problem is internal as you have no way of easily isolating the external network from the internal wiring on LJU master sockets.