It sounds like you are starting to have alternator problems. From my experience, the light only flashes if the alternator does not produce any charge. Whenever the brushes on the inside of the alternator are starting to go, or the voltage regulator is starting to fail, the charge light will start flickering/flashing in a somewhat regular pattern. If the light is flickering in a very irregular pattern, check the fuses, belts, all wires and connectors for corrosion, and the dash bulb itself. I would suggest that you check your alternator output. Autozone comes to mind, since they are doing a lot of free checking and have most of the replacement parts.