Try them on the feed from the solar charge to the battery first. Doubt it would be in the solar panel feeds but it could be. If those don't work then not much else you can do. Bet you have a PWM charge controller.
Disconnect the antenna from the radio and see if the noise is still present. The outcome of that gives you a direction. If it goes away it's radiated RF from the controller and you need to address it different than if the interference is still there with the antenna disconnected, which means its being conducted through the power.
It could be any type @Hillbilly Heaven, they are all switch mode, but you may be implying it's lower end quality and that may be a factor.
Also, more details might be helpful, controller brand and model, proximity of controller and radios, etc. Beyond trying snap on chokes you should check the connectors on everything are still sound, that you haven't inadvertently run power and coax cables immediate next to each other for long runs and that sort of thing. Also make sure you run the power feeds for radios, both power and return, all the way to the battery.