Take note of where the Capacitor (Referred to as a 'Condenser' by some) is in the drawing.
Adding one of these will help your problem, and should be under $5 at any parts store.
Make sure the case of the capacitor is grounded.
If you are getting a 'Snapping' sound, take your distributor cap off, and use a dab (light coating) of dielectric grease on the rotor nose, the cap center electrode (button), and the terminals inside the cap.
Sometimes corrosion or cheap cap terminals will cause the noise.
Dielectric grease is also called 'Tune Up Grease' at the discount auto stores. About $2.
Make sure all of your spark plug wires are well connected to both the cap, and the plugs.
Good wires will make a 'Snap' when the make proper connection.
Check to make sure the coil wire is connected properly. This is the source of the 'Buzz' some people hear.
Check your engine ground.
If you ground strap to the engine isn't getting good connection, or if the ground is too small, you will get radio noise.
Make sure your antenna cable isn't near a spark plug wire....
So many cats, so few recipes...