The DNS-323 also has cooling vents - that's what gunrunnerjohn enlarged - and incidentally, in so doing he has disrupted the designed air flow pattern.
I invite those of you who are brave enough to disassemble your DNS-323, there are rubber plugs on the back face that cover the screws holding it in place, and once that is removed there are more screws that hold the inner assembly in place, remove those and then slide the assembly out the front.
Take a good look - the system board acts as a divider between the upper & lower chambers - upper, where the disks are housed and lower, where the board & electronics are housed - air is drawn through the vent, through the lower chamber into the upper chamber and then out the fan.