The 'quiet line test' here's some instructions
The BT line test facility can be accessed from any BT dialling 17070.
Quiet Line Test
Unplug any extension phones, extension cables, answer machines or fax (anything except the phone you will use to do the test!). Or as OLD suggested unscrew your master socket and test from inside with a known good phone. First test from each internal socket.
Dial 17070, press option 2 (quiet line test)
You should hear 'Quiet Line Test' and then silence, there should be no pops, clicks, whistles, buzzing etc. If there is noise on the line, make sure it's not your phones connection to the socket (wiggle it about a bit) and that you are using the master socket. If you are sure its the line making the noise then dial BT and report the fault, they should be able to sort it out. Remember that 'mis-reporting' a fault (e.g. if it turns out to be your phone, extention cord etc.) may be charged a call-out fee by BT
If it doesn't work You have caller line id (CLI) blocked, if this is the case then on dialling 17070 the message will include 'there is no CLI detected for this circuit'. You can get round this by dialling a prefix before 17070, the prefix is 1470, so the full line test number will be 1470 17070.
Be aware that a favourite failure can be the ADSL filter breaking down, especially if you have the BT master socket conversion with filter included in the socket as opposed to the filters you plug into your sockets.l
The fault could very easily be the dropwire or water in a joint the point is you want to eliminate everything that could be considered your responsibility. The next hurdle will be the awful 150 interface. Once you get an engineer round be nice to him give him a cup of tea/coffee explain exactly what you have tried, and invite him to double check your findings. It's also entirely possible it's a line card fault in the exchange in which case the Openreach engineer will have to hand the fault back to a control and it will be handed out to an internal faultsman. The two are no longer allowed to communicate by regulation.
Alan