I'm sure you're correct, the knife switch does act as an antenna in
some way. For my current setup, I have unshielded lead-in line which
is acting as an antenna also, so the knife switch's noise input is
trivial.

I live in a rural area of New Mexico, in an adobe house. My radios
are far from my TV's and the only real noise I contend with is the
electric clothes dryer. Lucky, I guess.