How can conducted noise from an automobile battery charging system be suppressed?
Why Alternator whine is conducted noise: RF hash generated by the rectifier diodes and regulator rides out along the DC wiring into the radio. Ferrite chokes clamped over the charging leads add series impedance at RF while passing DC current untouched, so the charging current flows normally but the hash is attenuated. Bypass capacitors to ground can help too, but they must be in shunt, not in series with the lead.
Watch out Putting filter capacitors in series with the alternator leads would block the DC charging current entirely; capacitors used for noise filtering are always connected from the lead to ground, in parallel.
Ferrite in series, capacitor to ground. DC passes the ferrite, RF does not.