Could be a REIN issue, something you can check yourself
Tune a radio in to MW 612khz and if you hear a loud buzz it is probably interference from an electrical source
Faulty thermostats (Central heating, Immersion heaters).
Electrical power supply units (Laptops, Routers, Plasma TVs).
Industrial/Commercial power usage (Electric Railways, Electric fences, Electric motors).
Decorative electrical items (Christmas tree lights, Touch lights).
Security systems (PIR lights switching on and off).
Digital Communication Receivers (Satellite and Freeview set top boxes).
Internal power and telecoms cables run close together at the End User.
Not an exhaustive list, but something to think about