Very wideband Zener noise sources are a common piece of measurement equipment; and many folks built their own noise sources (also for RNGs) using Zener junction

Very wideband Zener noise sources are a common piece of measurement equipment; and many folks built their own noise sources (also for RNGs) using Zener junction breakdown. While building my own I needed quite a bit of shielding to avoid interference issues by RF sources (mostly HF fluoerescent lights and LEDs), so these sources might be susceptible to bias by EMI...? Other junction breakdowns have noise as well, resistive noise is very low power. Atmospheric noise and background noise is a thing too, but I'd guess they are too susceptible to interference by malicious actors...