@Prntckt All good things to know. I too have the radio connected a second battery, but I grounded my antenna wire to the frame. I will ground it to the ground side of an electrical system. Thank you again. I'll try the grounding the antenna first.
Do not run your antenna cable along or near any other electrical wiring (OEM harness, LED whip lights, etc). Keep it as isolated as possible.
Also, do not "loop" any excess antenna cable. Cut it to the proper length needed and add a new connector.
These two things are very common install mistakes that lead to interference.
Also, after first installing my antenna on the flag/antenna mount in the ROPS, I relocated it using a proper mount from Axia Alloys. They make great products.
Documented my full install starting
here.