You may want to check in the Technical Manual what was the suppression kit for Becker for our cars. I would dare to say you do not need all of those items, but the proper condenser at the alternator and good grounding are important (radio, hood, antenna, radiator).
The thing next to the hood lock mentioned in the previous post is called "Bronze Spring Thing" on this forum - when you search it, you will find it. I bought it from Authentic Classic a couple of years ago.
But honestly: my radio stopped making noise after sent for overhaul to the SL Shop. It was internal radio issue.