gar187erI do this for a living
ive seen AM signals picked up THROUGH the EMTA itself, radio tower was 400' from customer and they were in a metal building. go figure.
but yes this is an analog issue thus it has to due to with your phone wiring. I would see if you can isolate which line is picking up the signal, so you dont have to rewire the whole house.
I'm better than you!