I have a 100Base-T hub and I found that by putting
ferrite cores on EVERY line, power and data, really
quitens things down. The ferrite will stop, or reduce,
common mode emmisions which is the main noise
source. The CAT5 cables are twisted and are
transmission lines with differential RF, and don't
radiate as much, in that mode, as commonly thought.
I am also a ham, and while I don't transmit very often,
I found that my IC28 would cause the router to lock up.
The ferrite split cores stopped that problem as well.
Terry