How often to change sd starter jar--mold?

[moonlightinvt]

I have had sourdough starter on my counter covered with cloth napkin for about 4 weeks now. I have changed the jar three times (when I've made bread). The first two times the jar appeared to have some mold inside where the starter had dried (above the batter line from when I stir it).

Is this typical?
Should I be changing my jar more often?
Should I discard the starter and start all over again (is it safe)?

TIA!