Ofcourse proper network cables are twisted in pairs and shielded for a reason: so no signal gets in, but also next to none comes out. All the copper in your house essentially acts as one big antenna if you use these powerline communication boxes. You would not believe what the spectrum looks like next to one of these houses. Ask any HAM operator, they have a deeply rooted hate against these things.

Thank goodness they seem to die out slowly since powerline communications doesn't seem to be able to keep up with increasing broadband speeds. As it turns out you need proper network cables to get halfway decent speeds.