Such a problem happens often here. The cable company delivers subscriber boxes with bad power supplies. When some component is blown, the PSU stills delivers power to the box, and he subscriber sees nothing particular. But the PSU then sends very strong harmonics of the switching frequency on the mains. It happened two times at my neighbours's (with strong QRN to MW and SW frequencies, which are also the frequencies of ADSL on the phone lines). The second time, there were many ADSL subscriber in the neighbourhood that lost access to Internet (I suppose those on the same phase of the power line). And that was 24 hours a day for several weeks each time! The cable company also is an Internet provider and gained new subscribers that way! Let your hardware jam the other companies using the phone wires!