Are you possibly mistaking it for noise coming from the cooling fan that is inside the unit? Mine doesn't make much noise at all, but I know there is one. Not sure if it runs constantly.
If you have a loud annoying sound, maybe there is an issue. Can you post some audio/video?
Roamio Pro, wired ethernet
Mini using MOCA (from the Pro)
on Cablevision Raritan Valley system (Central NJ)
w/ Cisco PKM803 CableCARD on firmware 184.108.40.2061
*** 2013 newbie to Tivo ***