On all Tivo's, the hard drives and the fans run 24/7. No turn offs.
Everything sounds pretty normal, although it's possible for drives to become noisy with age. Noise may or may not be a sign of impending drive difficulties, including failure.
If the drive is an original Tivo drive and functioning properly, it's probably about as quiet as it can be.
Make sure to clean the fan periodically and keep all the vents clear for good air circulation.
Go into settings>account and system information to check temp. It will tell you if temp is normal.
I guess you must use in the bedroom. My 2 units(SD-H400 & 540040) are in the den and don't bother me, but they are not totally silent and both are modded with large standard drives. I imagine if they were in the bedroom or any quiet room, they would be more noticeable.