Tony, that thing is always on (I own two Hughes DTivos). The one in my bed room is noticable because it's not in a cabinet. However, if you plan on mod'ing your DTivo (I can just picture you opening the door for the UPS man with a screwdriver in one hand and needlenose plyers in the other) then there is an easy way to install a quieter fan.

In fact, the 2nd gen DTivos require a mounting braket for additional drives. This company sells kits that include the brackets (nice design btw), all needed power cables and a quieter fan. It's called the TwinBreaze. I ordered mine, and got great service, but all of the install tutorials for preping a HD aren't writen as well as the empeg one.