Dash turn indicators acting up

Had this problem for long but never paid too much attention as the blinkers work just fine, it's just the green indicators in the instrument cluster acting weird. Hope someone can suggest where to start.
When I have no lights on, everything is normal, the indicators work nice and bright. When parking lights or headlights are on, indicator goes a bit dim and the other direction one starts blinking too, as does the red high beam indicator as well. Outside blinkers still work normally. Occasionally this symptom goes away after driving for a while but not always.
Must be a bad ground somewhere? Anyone had this?