Hello, if it buzzes when the engine isn't running, perhaps check the earth/ground connections at the radio, amp and aerial, and the connections between them. Could also be a damaged or bad speaker
Depends where the buzz is coming from
If it only buzzes when the engine is running, then check the above, but could then also be a bad suppression component, could be a long job checking or replacing all of those, there are details in the tech manual under radios/suppression