So how do these sources of noise show up on the cameras? Visible lines of distortion? Lack of recording?
Depending upon the type of interference and the intensity of the same. It can be seen or heard as wavy lines, bars, odd colors, hum, buzz, popping, strobing, haze / snow, etc. Anyone with the proper
tools can detect interference whether that be a 10K oscilloscope to something extremely simple: Radio, Florescent Bulb, Cell Phone, etc.
Keeping in mind RFI vs EMI is not the same but at times result in similar observed behavior / problems.
If a vehicle is leaking any high frequency radiation a common florescent bulb will immediately display the same by flicking. In the same vain if RFI is present if a radio is tuned into a empty (AM - FM) band the common background hiss one normally hears will show case anything from popping, extreme hash / hiss, whirling, as you move to / or away from the generated noise.
Regardless of the above more often than not problems seen at home, in business, in the industry is due to improper grounding.
Whether that be due to ground loop, poor grounding . . .
Poor grounding can be as simple as the ground is a poor conductor: Sand vs Clay
Ground rod not driven deep enough, star washer not used, pole mount is used without a dedicated ground strap to ground rod (not 8' or longer), corrosion, plastic on metal.