Easiest thing to do, then is to try a phone directly at the demarc jack, with the house connection removed. If there is still noise there, then its the lines coming in, not much you can do about it. If the noise is not there, then something is wrong inside the house. Try to isolate the branch that is giving you trouble inside the house.
It doesn't take much sometimes to get static on a line, even a corroded terminal, or a faulty jack. If the outside line to the CO is wet, or faulting to earth then you will definitely get static, and the Telco should fix it.
It's often not a priority to them to fix line drops to a house, but keep calling and hopefully they will repair it. Sometimes it's a case of them knowing full well that a line or area is bad, but they also know it may be a big job and they are just putting it off.