There is no hum problem on mine
99% of the time when people get hum, it is likely due to other equipment and the cables.
If you want to make sure your Firepod doesn't have a grounding problem, maybe you can do a quick test before you buy:
1) Plug in power and power on the Firepod.
2) Plug in your headphones, and nothing else.
3) Turn the volume up until you can hear the usual slight hiss.
4) Turn up the gain on each preamp channel, one at the time. There should be some added hiss, but the hum should not be louder than the hiss.
5) Repeat for each preamp.