JThat "RF noise"--radio frequency buzzing and humming and static--can radiate for miles, interfering with all kinds of equipment, but most notably any kind of radio receiver.
It's been six or more years since I did so, but - IIRC - my Lumatek 400-watt ballast produced a few new birdies when checked with my 25mHz - 1.3gHz scanner. At the time, I was pretty paranoid about it. I don't worry so much about that particular thing these days, but if I was running unshielded electronic equipment in a grow, I'd probably do a scan through the AM and (88-108mHZ) FM radio bands. More out of courtesy to the neighbors than a sense of paranoia, though. Around here, folks don't really seem to complain to the FCC unless someone is running a 1,500-watt linear amp on their CB and their transmissions are coming in over people's kitchen clocks or something. Back in the early '90s, a semi-local truck stop used to read their dinner special menu out over the CB and it could occasionally be received a couple states away. They did so for a couple years before getting nailed - and they proudly announced who they were and how to get there each and every time they broadcast.