Battery charger and also stray RF. Try some snap on ferrite chokes or an rg isolator or Low Pass Filter at the radio. The Low Pass Filter in combo with sole ferrite chokes or a 1:1 balun or RF isolator should resolve your issue. Might be time to get a power supply. The megawatt power supplies are worth every penny. I use the s-400-12 on an Icom 746, voltage set to 13.85vdc. And it's adjustable from 9-15vdc. They make a smaller unit. 30a vs the 36a one I have. It's only $50 or so. Plus shipping. The one I have is only $60 and he also carries a 50a one that can be ran in parallel with 4 or more of them connected together for increased amperage. No bridge needed. Just make sure voltages are same. Anyway. JMHO. But if possible, get a power supply. Check your local CL as well. You'll need a 15-20a one for the radio you are using. The more amps the better. But I would try a LPF, (low pass filter) after the radio and see if that helps. Sounds like you have some stray RF. Hope you get it resolved. Try unhooking the batt charger and turn the power down on the radio as to not kill the batt to fast and see what happens as well. Just some more food for thought. Again, hope you get it resolved.