Why the STB makes Noise

From the Motorola FAQ:
Why does the set-top continue making noises even when it's turned off?
"Like some other appliance in the home such as your refrigerator, the set-top needs to remain on at all times to connect with the cable plant headend for continued exchange and refresh of data. The DVR set-tops have an internal hard drive and fan which remains on at all times. You will experience a slight humming noise during operation. There is no reason for concern. Again, similar to the humming from your refrigerator, this humming from the DVR means the box is on and running to serve your entertainment needs."

And it uses energy like a refrigerator too...