So back in my high school and college days I was a Technician at a CB shop (remember the 70's!) Then I owned a commercial two-way radio (Police, Fire, Taxi etc) business for 40 years, so I've had a bit of experience here.
If you hear a "whine" that varies with engine RPM, then you are looking at alternator "whine". This is caused by a faulty alternator or battery with a weak cell. You might get rid of it with a choke and capacitor on the power lines, but its better to fix the cause. I've had many an argument with mechanics on this one.
If you hear a "Hash" noise that does not change with the engine RPM, but does change with the dash fan speed, then you are likely hearing RF noise generated by the dash HVAC fan motor (even the rear suspension compressor or windshield fans motors can create this noise). This noise is introduced through the antenna and no amount of filtering on the power line will fix it... you must suppress it at the source. GM installed a Feed-Through capacitor on the power lead of the dash HVAC fan motor to suppress this, but that capacitor is likely dried out, or gone completely 50 years later. Feed-through capacitors are not as common now as they used to be back in the days of AM radio, and tend to be rather expensive. If this is the noise you are experiencing, try installing several points ignition "condensers" (another name for capacitors) from the fan motor power wire to the ground (case) of the motor.
If you hear a "Tick-tick-tick" that varies with engine RPM then you are hearing ignition system noise. This noise is also introduced through the antenna and must be suppressed at the source. If you have a "Noise Blanker" switch on your CB, turning it ON should reduce this interference. If your ignition wires are old, they should be replaced as that is the major cause of this noise. If your ignition wires are not "resistor" wires, then you need to change out your ignition wire to radio interference suppression resistor wires (this isn't a dragster). There may also be a "condenser" on the positive side of the ignition coil to ground if you have points ignition that can be replaced. If you have HEI ignition there is a condenser that could be faulty inside the distributor beside the ignition module.
Noise Blanker (NB) is a circuit that tries to get rid of ignition noise by receiving the same ignition noise on a different RF frequency and inverting it, then adding it to the audio path so that it cancels out the noise.
Noise Limiter (NL or ANL) simply limits or clamps the pulses of the audio noise so that the noise is not louder than the desired audio. Its usually just a couple of diodes in parallel in each polarity direction.
That's all for now.
