a digital ballast will be quieter than a magnetic ballast.
digital costs more to buy.
the ballast can be made remote.
if the ballast is in the same room then once you turn on an oscillating fan you dont hear the ballast anymore. so basically the fan is louder.
oh yeah your exhaust fan will cover up the noise of the ballast also. lol
i really dont know how people can do a stealth grow. im just grateful that smell and minor noise isnt a problem for me.