Plugging the home phone into another phone socket within the home (if available), tests to confirm if the fault is caused by the internal cabling.
1. Disconnect the home phone / ADSL filters from the current phone socket.
2. Locate all the alternate phone sockets within the home.
3. One at a time, plug the home phone into each of the sockets.
4. In each phone socket, pick up the handset and check the quality of the dial tone then, if the tone is clear, attempt to make a phone call and check the quality of the line.
5. Repeat this process until each phone socket within the home has been checked or the issue has been resolved. If any of the alternate phone sockets have no issues, it means there is an internal cabling fault.