A slight flicker to the interior lights seems to be normal when the door is open (my Dad's new Toyota does it worse than my Mystique). Check battery voltage while car is running, you could have a problem with connections, corrosion, if the voltage is wildly fluctuating. The voltage should be 13.8-14.8, if much higher the alternator is 0vercharging, if around 12.8 or less, it's not charging.
