We also have a ZD 3000, and the two fans in the back center of the unit stay on full speed during operation. The PSU fan and the one on the other end appear to slow down. The unit is in a 67 degree server room, so I don't think it's overheating...
Is this the normal operation for this unit? It is far louder than any other device in our server room at present.
These descriptions are of course subject to some amount of subjective interpretation, but the consensus here is that this is not normal - you should hear the fans throttle back from the initial high-speed at boot.
My recommendation is to open a support case about a potential RMA.