One of my old trucks does this. Converted from an external regulator to an internal (Delco 10si) type alternator. Mine had the tick before and after. The headlights were not effected but the dashlights would dim a little and the volt meter would "tick".

Is the power to the headlights running from the battery, through the dash, to the switch and then to the headlights? Installing a "bright light kit" for the headlights might fix their pulsing. This bypasses a lot of wiring and the lights can be powered directly from the battery.

Never figured out the cause and called it the truck's heartbeat.