I have just got a new V+ box and mine hums too.
The only thing that I can think that it could possibly be is that there could be a fan in there to keep the hard drive cool,because I have the same thing with my compact PC.
You do get used to it after awhile.
I have seen on here someone saying that their Sky+ box hums too, so I don't think it's just a virgin thing.
I don't know about you but the light when it's on stand by is quite bright too, you you would think in this day and age when everything is all about the carbon footprint they would have done it abit different.