Very often such noise could be improved with
a simple task, the first thing to try is connecting a bifilar wound choke where
your telephone line enters the house. the next is to improve at your neighbours.
Very often the balance is not what you might think, I've shown some of my own
experience from telecomms on http://www.noding.com/la8ak/12345/n11.htm
A bifilar wound choke passes the balanced
signal, but attenuates the unbalanced. Propose to wind a 2x 1mH choke (possibly