Two ways noise gets into the radio. Via the antenna or via the power lead. Disconnect the antenna at the radio, if there is no change in noise, it's coming via the power lead. Maybe need an inline choke (easy to make). If the noise goes away, it's coming via the antenna which means you need to check your RF suppressors (if fitted) or fit some if not. That's how we handled this sort of stuff when I was an apprentice radio tech years ago, installing/servicing two way radios when they were as big as shoe boxes! Of coarse you first check all antenna and radio connections are clean and secure.