There is no mechanical hdd that are completely silent, some are quiet, only an ssd will be totally silent, that said, there are some that are very quiet. I just bought a WD RED 3TB for my synology DS111 and i cant hear the hdd at 2mts, i hear more the little fan, that reminds me i gotta do something about it... =(
I had good experiences with Hitachi 2.5 hdds, from the 5k500b (i still have 3 of this running for 3 years on laptops and htpcs), very little vibration and i personally dont hear them, but i had a little bad experience with the 5k750, it made a screeching sound every like 1hour or was very annoying, i moved it to 2.5 external usb3 enclosure and works pretty well there. On my main desktop, im running a Hitachi 7k1000, that to me its prety quiet aswell, but vibrates a lot more than my past 2.5, but expected for 7200rpm. I recently upgraded my download station and one of the my external 2.5 enclosures to the new Hitachi 5k1500
, and vibrations are low and noise... again to me its very quiet, but this could vary from user to user and sample to sample. It been bought a lot recently, specially by PS4 users, lots of good user reviews, that dont tell much about how it is in terms of noise, but its a pretty reliable hdds, at least that two that i bought no issues for 6 months now.
I would probably give a try to hitachi 5k1500 or the WD 1tb red, whatever you feel might be better, for me on 2.5 it always been hitachis on my laptops, they have work really well for me, and i tent to stick and reward companies that deliver a good product, so that's my suggestion. You do have to accept the higher access time being a 5400rpm drive and laptop drive it will be slower, but thats how things are, on pure raw transfer rates they can saturate a gigabit lan, so for what i use them they are fine, i'll leave you a CDM of my 5k1500,