Think I would be checking the wiring between the incoming socket and the phone cradle or hub Foxhaven. Particularly the microfilter(you do need one) which should be an ADSL microfilter. In the past I have had problems with tarnished contacts and changing the filter sorted it. You could unplug, and inspect, then try plugging back in again to see if you get a better connection. You will be able to see if the contacts are tarnished, they will be black instead of a gold colour.