Sting
Ghost in the Machine
Actually, 4 pairs (8 wires) in my case. When I had a noisy line the telkom chappie also tried swapping pairs and eventually replaced all 500m that runs from the street pole up the drive to my house - 6mm black cable. Didn't help - turned out to be water damage at the exchange.
That will be the exception, not the rule.
You will find many cases like this, as they sometimes run out of stock of "drop-wire" and then use the next biggest cable size available!