Have you or anyone made any wiring changes lately in the house, anywhere? Do you have a leak somewhere, maybe caused by winter snow & ice? There are lots of those this year.
You probably have a short circuit in your wiring somewhere in your line. You can still hear because phones do not require a such and absolutely-constant flow of electricity like other electrical appliances do; they can transmit static. It could also be due to something finally giving up the battle against time, such as a slipped connection or, as suggested above, a poorly insulated wire. Even a bump against a wall could have slipped the connection. If you cannot find the short, a phone technician will have testing tools that can help pinpoint the problem far quicker than you could do on your own.