Powerlines can have defective components and will generate RF interference. In Canada I have called BC hydro and they met me and aimed a "gun" at the poles and got a high reading. They replaced the bad component and the RF interference was gone. This was job related not RC planes. Industry Canada or FCC in the states regulate these things and take complaints quite seriously (espesially in regards to "private" radio channels). You could try a call to your power company - just try not to let on that it is for rc planes, just say that you have a rx that is getting "hit" and you suspect their power lines.