it is a double master socket ,i presume the socket is fitted on an exterior wall and the dropwire goes directly into the rear of the socket,if it is constanly noisy it is straight forward to locate problem.if it is proved underground the engineer will swap onto a different pair of wires in underground cable to exchange,unless there are no good spares to use then it will take a little longer for an underground engineer to resolve.just double check all your kit….i am still suprised how many people dont, and are shocked when they receive a charge.and openreach charge your service provider not you..