Tread carefully. Be certain the fault is outside before you get BT involved. If they come out and the fault is inside your property, they will charge £130 plus £90 per hour to cure it, so, as the the builder boys have said, unplug everything, and really, in case you don't know, you should remove the small faceplate from your master socket and plug a filter into there, and then plug a phone into that and your hub/modem and see if it works o.k. if it doesn't, then make sure the cable feeding that master socket goes directly to the master socket from the outside connection, and that there are no cut ins on it and it has not been damaged. only then are you safe to call out Bt. also, try a different filter, just in case, as they also go faulty.