Having tested various buck converters including LM2596-based ones, all I can say is that when it comes to RFI, they are not all born equal. Some are a nightmare while others are quiet. The problem is that you are unlikely to find any source telling you which ones are quiet and which ones are not. They are generally pretty cheap so you may need to buy a few before you find a quiet version 
I like the Bioennos that the guys in NA use. I like the fact that they have a PCM included. The only caveat is if you use them with a solar panel and a charge controller. The battery’s PCM and the charge controller (depending on the type) may compete with one another and generate an alternance of high/low volatages. You just have to be mindful of how you wire your set-up in order to avoid this problem.
Since not many people use solar with those it should be a non-issue for most.