I have had the same kinds of interference problems with a
hub I have and the Ethernet cables.  If you can, try to route
your cables near the floor if they aren't already and this can
help some.  I am lucky enough to have an outside antenna and the
problem is not bad at all, but I certainly hear lots of computer
noise if I do use an antenna in the house.

        As for the Ethernet cards, the 10 megabit cards produce
carriers from 10 megahertz all the way up to and through the 220
MHZ band.  You can even hear the buzzing of the data if you
listen to some of those frequencies.  It is a good data
transmission indicator at times.

Martin McCormick WB5AGZ  Stillwater, OK
OSU Center for Computing and Information Services Network Operations Group