The product is producing a fairly audible buzz when is plugged to the mains and irrespectively if the computer is off or on. I am almost certain that I can hear the power supply cooling fan spinning when the Mac as well. Again, it doesn’t matter if the Mac is off and the thunderbolt cable is disconnected. The noise is still there. When the computer launches, the HD fans kick in and they just mask that noise.
Do these imply a problem with the unit’s power supply? I haven’t heard any of my previous RAID drives making such a noise.