I just got my Thunderbay 4. It came with a Zalman fan. I have it loaded with a SSD, two 3 tb drives, and a 1 tb drive. It's currently sitting on my desk, just next to my monitor.
I have to say, it's pretty loud Definitely not something that blends into the background. Some of it is the typical hard drive noises, but most of it is the fan.
I think short of putting it in a drawer, it's going to be loud.
I may consider the fan replacement.
Otherwise, it's been working fine and seems to be constructed pretty well.
Change the fan as I and others have noted in this thread and it becomes noticably quiter....not silent but much better