If you connect phone to the test socket does it work and assuming it does then try quiet line test. Dial 17070 option 2. Should be quiet and best with corded phone if cordless then dull hum normal
Your master socket is first socket in your home where phone wires enter your home.
This link suggests there is a dry joint and you need an enginer. http://www.filesaveas.com/jarviser/hubtrouble.html#type9