How loud is the ReadyNAS 3220???

That's going to depend on how cool you keep the room and how much work the NAS is doing.  The warmer the room (and the 3220 does create a fair amount of heat) and the more work it's doing, the faster the fans are going to run.  During a RAID sync, scrub, or balance, the load will be higher and it's going to run louder.  That 30dB is likely when the NAS is "at idle".  I've got one that's a spare in case one of my other units fails, and it was noticeable that it was running when I was checking it out, but it wasn't as loud as my older RD5200 and RN4200V2 units.  30dB sounds like a pretty low volume compared to what I remember.  

The small power supply fans are the biggest offender, mostly because they have a higher pitch.  If you simply don't plug one in, you have to edit the config to keep the OS from complaining.  You can pull one of them, but I don't remember if I still had to edit the configuration file to make the OS stop complaining about that (on the older units, pulling the supply was sufficient).  I never found a blank to put in place of a supply, so you'd have to figure out what to use to cover the hole or just leave it in and loose.