Woo Hoo - a mold issue in Charleston, my favorite problem 
maybe cause it’s been raining and the humidity is high, and you’re in a flood zone so the water table is high, the vents are to let flood water drain out instead of crashing the walls
for non-flood times, like now, the vents simple allow the air inside and outside to stabilize quicker, the only way to prevent the mildew is to reduce humidity
stop/slow/control/reduce the air inleakage and then dehumidify, the tighter the seal the less dehumidification you’ll need
put some type temporary seal over the vents, if possible paint the block walls, then add the dehumidifier, resist the temptation to set it real low, just get it down to, let’s say 60%, try that and see what happens, you may be able to raise it a little or need to lower it a little, the higher you set it the less it will run, pipe the drain it to the outside
PM me if you want more details, will be glad to help
Pioneer 197SF