Hi Professor,
I *used* to use Mains-Networking, but found it to be too unstable.
To mitigate my interference at the time (I was also using Marmitek X10 systems), I fitted a Marmitek FD10 Phase Coupler/Filter to try and control it.
Like I said, I don't use any of that stuff any more, but you can find out about the filter here -
http://www.marmitek.com/en/pdf/08934.pdf
TBH, I don't know if it ever made a difference, but it seemed like the decent thing to do.
There are other filters out there that hopefully will cut down on the muck that gets injected back into the mains!
Sadly, like light-pollution, airwaves-pollution is a bane of our times.