Seems a lot of cams are still using 2.4ghz analog transmission, which is going to be worse today than it was 15 years ago when they started... everyone and their sister uses WiFi these days, or bluetooth, which are both on the same band as wireless cameras.
I've been looking for an affordable DIGITAL transmission camera setup, but haven't had much luck. I am working on weather-proofing some WiFi cameras for using on my RV... a bit more complicated to use, but should be less prone to interference and they're cheap.