My provider did a line test when i was having problems recently and reported a fault on my line i proceeded to check all my equipment and connections and did the router into the test socket test to see if it would solve the problem but didnt, I even asked BT to check the line and to my surprise they said there was nothing wrong with my line on both the occasions with just the router/filter setup plugged in and also with nothing plugged in!
I knew something wasnt right as it was impossible to make a phone call even with any phone in the test socket due to excessive crackling on the line.
Eventually I took the risk of allowing a BT engineer to visit even though I was warned that if no fault on their part would have me face a hefty repair bill. Though I was 90% confident that it was a fault up to the test socket. Also I suspected the "old" grey incoming cable as the new cable they use is black sheathed and indeed the engineer put his fault tracer on the line and informed me the fault was "19 feet or metres"(??) away from the house and he'd replace the cable, problem solved!
