1st find your main socket,if unsure follow wire from outside,if it is a nte5 split socket,remove lower part(if you have extensions this will disconnect them) to expose main test socket inside,plug in a known to be ok corded phone and do above quiet line test.if it is noisy at the test point,look for damage on internal/external cable before master socket.Also check for verdigris on adsl spliter where it is pluged into socket and on portion of nte5 you have removed.
If it is noisy/crackly with test phone in test socket,and no obvious cause can be seen,ring your service provider and report line noise,this is likely the problem with bb.
Not that horrific was it 🙂