[Al Skierkiewicz]

Invictus,
The sound should become less noticeable when you connect the radio. Without a load, the circuitry is hunting for a good operating point. When it does that, anything that is not tight in that circuit (transformer windings, magnetic cores, even flexible wire) will emit energy in the audio spectrum. This is a good reason to tell people to not mount the regulator near or on the radio. There is a lot of RF hash emitted by that little box that can affect the wireless link.